I feel like I spend literally 80% of my day yelling at/bribing/threatening DD1. It seems to be over everything, cleaning up toys, getting ready for bed, eating dinner, getting buckled in the car. It's driving me crazy. We never really needed to do time outs and now she doesn't respond to them. For example I'll tell her to clean up her dollhouse. She'll ignore me and probably get another toy out. I'll take the new toy away and tell her to clean up the dollhouse and she can get the toy back. She'll tell me to go away or she'll throw a screaming crying fit. It can take a full 45 minutes of me staying within arms length of her to get the dollhouse cleaned up and with a 1 year to watch (plus I babysit a 4 month old), I don't have that kind of time. If DD2 is being laid back and I can focus on just DD1, it is literally a back to back thing and I am exhausted by lunchtime. Like I said, I can threaten to take away the toy or no outside time or early bedtime or I can try to bribe with candy or ice cream and nothing is getting any response. I'm going crazy here. My DH comes home from work and within 2 hours he is tired of being here because we are constantly yelling at DD. Help?

Re: Please help
We have learned to set a clear limit and also telling ds1 what the consequences will be if he does not follow through. This allows him to make a decision about follow our direction or continue with whatever he is doing knowing that he will get the consequence we laid out for him. Other times, we have told him we will count to 3 before xyz consequence will happen. Again, gives him some time to think about what he should do or deal with the consequences. There are times that he will do numerous things in a matter of 5 seconds and we can't give him a time-out and take toys away, etc. We just bundle it together and give one consequence. It is tough and there are days I am screaming lunatic, too. Good luck and HTH!
We've found that empty threats do absolutely nothing with DD. Are you following though with these threats? I think it is essential for a kid to know that if you say there will be a consequence for her actions, that the consequence is actually performed. Otherwise, she'll know that you will yell but not follow through. Also, I agree with pp that we have only a few hard and fast rules per se. There are a couple of things that are an instant time out (we're lucky that she responds really well to them) like biting (we're through this stage now), spitting (her current favorite) etc. Otherwise, we focus on generally listening to what we say. We also try to be active participants in what we're asking her to do. If it is to clean up a game, we do it with her but she must help. We try to avoid the "you do this DD" and instead "we are going to do this DD." I understand this can be hard with other kids around (we have a newborn), but leading by example works really well with DD. Plus, it gives her a few minutes where the focus is solely on her, which is now even more important with her sister around. Once her task is done, lots of praising. She LOVES hearing "I'm so proud of you for doing XX."
It sounds like yelling isn't working for your DD. There are lots of books out there on discipline. I don't have any recommendations but maybe a trip to the library might yield something more helpful. GL!!
The pp suggestions are good. I have found that dd can't "clean up" by herself. She gets distracted or it seems too overwhelming or whatever. We clean up together, we sing one of several clean up songs and do it together. I often say something like "We need to put X away before we can do Y. The sooner we do it the sooner we can play! Lets race! Who can do X the fastest?" Or "What do you want to put away first the babies or the food?"
We clean up each room before we move on to the next one, or each activity. Aka, we color, then put it away and do puzzles, but with general toys I don't do clean up time until we move locations. So the playroom often looks like a bomb went off.
When we leave we usually check out how pretty we made it look. Also, there is generally a reminder if we can't take care of our nice things they get broken, lost, etc and we shouldn't have them. I rotate toys, putting some away and bringing others back out. And I often go through the toys with the girls and toss/give away ones that aren't being taken care of. I have said "If you don't put it away I'm going to throw it out." And I did it (It was a couple of toys from Mcdonalds that we got on a road trip, but hey the message was sent loud and clear)