I don't have much advice except listen to your body, though I'm sure you're better at it than I was because I am a FTM. But, in the early weeks when I was still working I was standing 8 hours a day, climbing ladders, and lifting heavy boxes all day because these were all things my doctor said was okay and the boxes didn't exceed my weight restriction.
About four hours into my shifts I would literally feel sick because I was so exhausted. I would get dizzy and light headed and I'd get a heavy pressure like the babies were trying to come out. After 4 weeks of this at my next appt my cervix had shortened to a 1.7, 3 is normal, and I had funneling. I was only 19 weeks along and I think my weeks of over doing it had something to do with it all. I could be wrong but NOW that I'm on bedrest because of it, I haven't had those symptoms and my cervix has hung out at a 2.
Just take it easy, at around 28 weeks it's probably going to be really hard on your body.
As far as raising twins, I haven't got that far yet :D but the other MoMs here on the multiples board are really great and are so informative. I spend a lot of time lurking and learning all the advice they give which has made me begin to feel a lot more prepared! Good luck and congrats x2!