MIL has been "offering" her help and hinting that she has plans to be at our place every.single.day. We *think* that one of the twins may be close to coming home. And she said the other day she. We were talking "Well I am going to be over there with you all the time anyway so if he is on any monitors or oxygen I am sure I will know how/what to do and you can just leave him with me and go to the hospital." I did politely say back to her "I appreciate the offer but I plan to take him back and forth with me or waiting for DH to come home to stay with him/go see her. And I really think for the first little bit we aren't going to have company because we are just going to be getting to know each other and his routine."
Her response was "oh I know I dont plan on coming over the day he comes home but the next day I will be there.
I repeated myself but she just kept going. She is just dying for us to leave the twins with her. The problem is that she is sick and has days where she can't get out of bed to take care of herself. And she is illness prone so I worry about her not knowing her limit and/or making the twins sick. She also has limited motor function and DH and I both feel like she would not be able to care for one let alone two infants.
I dont want to hurt her feelings but at the same time I feel like ground rules need to be set now before she takes charge or assumes it is acceptable to just stop by whenever (like she has mentioned she will do.)
I have asked DH to either talk to her directly or talked to FIL and let him explain things to her. And I have also said I will try to fins things that she can help with to try and include her, but I just dont want her around 24/7.

Re: need some advice WWYD?
I could have written your post! I hope that you get some great advice from moms who have BTDT, because I am going through the same thing with my MIL right now. It doesn't help either that she buys and buys and buys stuff for our little guy, so I think she feels like she has some *right* to access to him whenever she wants. Sorry, you don't buy access to your grandson.
Sorry to hijack your thread
 My DH and I plan to tell NOBODY that our son is coming home. If we get the news ahead of time, it will be the hardest secret to keep, but it's the only way we will get any time at all with him.  
Sorry to hear about your pushy MIL. I don't have any real advice on that.
Luckily, my twins came home the same day, but my NICU mentioned that if they didn't the one that came home can't come back in due to germs, etc. Just wanted to throw that out there. Yay baby coming home!!
My mom was like this when DD was in the NICU. It drove me batty. She would actually go to the NICU when I wasn't there. It really pissed me off b/c the doctors didn't want anyone to hold DD for several days, due to it stressing her out. So unfortunately we had to put my mom on the DO NOT ENTER list. Yes... I called the NICU.
Obviously your talking about after the babies come home. I would definitely have DH talk to his mom about her coming over uninvited. You guys really need to stick to the "no one is allowed over if they are sick" rule. I would maybe let her come over, when your around, but I would never leave the babies with her, if her health is an issue or her mobility.
Ugh, sorry you have to deal with this. Try not to stress out to much, and hopefully your MIL will understand that you all need some bonding time.
Congrats on getting close to home! One of my twins came home a full 4 weeks before the other so I know how hard it is. My original plan, which included term babies, was to not have anyone visit for the first week for the same reasons that you mentioned, but it wasn't realistic for us. To be honest with you, I needed help. DH was at work (he took off this week now both are home), the hospital is 45 minutes away and I was trying to adjust. We started taking Hunter to the hospital every day but quickly realized that it was getting to be disruptive to his routine and we weren't able to give Liam the attention he deserved. I may have felt differently if I thought they would come home close together, 4 weeks is a long time for a disrupted routine.
That being said, my mother watched Hunter not my MIL, because my MIL is not reliable. I had her come over one day when I stayed home and supervised, I was not happy with what happened. I told her she can watch him while I am home to let me get some chores done but that I would NOT leave him in her care yet. My DH is on the same page which makes things easier. My mother is also EXTREMELY understanding about boundaries and my MIL is not, to the point where my mother had to tell my MIL to not call her to complain about what we felt comfortable with in the NICU (no-one visited until they were off C-PAP).
It all comes down to what you are comfortable with, make sure your DH is on the same page and talk to her about your concerns. Let her know that there are to be no visits without invitations and remind her that although you want them to have a relationship with their grandmother they need a relationship with their mother first. You went through so much time where you were not their primary caregiver and you need to bond!
Good luck with your decision and I hope both your babies are home soon!
First, congrats on possibly having one of your LO's home soon. Second, I agree with Boston - make a list of things she can do such as cook a meal, laundry, watch the baby while you take a shower. And your DH needs to present that united front with you.
I didn't have any family members who were quite that pushy, but I know that my MIL and mom and some aunts would have been at my house ALL the time if I let them. I just told them up front that I planned to be very, very selfish with my kids when they first came home. I explained that I had waited more than 3 months to be able to care for them and actually feel like their mother, and that I (along with DH of course) needed the time to bond as a family and feel like parents. They totally respected that and I had no problems at all. Good luck!
ETA: I did, however, have my ILs and my mom particiapte in monitor training and infant CPR class with us. I knew that there would be times that I would either want or need to leave the babies with someone and I wanted to make sure those people knew what to do with everything.
Just wanted to add that my NICU was the same way. Charlie came home 4 days before Lily and we were not allowed to bring him back with us when we went to see Lily. DH and I just went in shifts - one would go see Lily and the other would stay with Charlie then we'd swtich later in the day. And we needed to have my IL's baby-sit Charlie when we went to the NICU to bring Lily home. DH and I wanted to bring her home together (and say goodbye to everyone) so IL's baby-sat.
You and your husband need to discuss with the rules are, and then very clearly explain to them to her.
You will probably need to be more direct than you'd like, but, she'll come to understand.
I hate awkward situations. Hugs!
I have this situation, also, where my mother is ill and has bad days where she's in bed or on the couch all day. Initially she also wanted to babysit. She is/was searching for ANY way to be of use not only to help us but also to make her life seem worthwhile yet. Anyway, I had to trust my instincts which was very hard. I ended up coming out and telling her that as the mom, I had to trust myself, and I just didn't feel comfortable leaving LO alone with her as her physical condition could change so quickly without warning. It was a very hard converation, and I know it did hurt her some to be in that position, but I had to do what was best for my LO. This is tough, tough stuff and I'm so sorry you're having to deal with it on top of having your babes in the NICU. Remember to trust yourself and your feelings and you will always do the best in any situation. Good luck.