Congrats Julsey !! I am 21 weeks with g/g fraternal twins. The nausea is due to the extra progesterone created with twins -- it is common and difficult. My nausea ended at my second trimester. I highly recommend eatting as much as you can now and especially when the m/s ends... you want to have two nice big babies born. While singletons are still able to gain alot of weight near the end of your pg, it is different for twin pregnancies. We have a harder time gaining weight near the end for two reasons 1. we go early 2. there is less room in there.
I have always mentally prepared myself for possible bedrest at 24- 28 weeks -- this means that you will need everything sooner. I spoke with a twin mom who had her babies at 26 weeks !!

Good luck !!
Heather