For the godfather it was nothing fancy... It's DH brother so we just told him. But DS godmother is our bestfriend and we invited a bunch of friends over for dinner and her boyfriend set up their video camera and we asked her and caught her reaction on camera. It's so funny to watch now. She cried and screamed and laughed and ran around hugging us all lol.
We just asked them. Nothing too special. I think they both knew because DH and I each have two siblings. We had one on each side for DD1 and then the other two for DD2.
We didn't do anything special for either. The Godmother is my sister and my mom told her we were planning on asking her before we got a chance to so I just called and basically said that I was assuming she was OK with it and she said yes. Godfather is a friend of ours and we tried getting together with him to ask in person but schedules weren't working out so we just asked him over the phone, he said he'd be honored once we explained what it was lol.
Re: how did you ask godparents?
We called and said "we would be honored if you'd be DDs godmother/father"
Thats it.