J.S.
I recommend transitioning in to the big girl beds first, and it probably really won't matter if they do that before the move, or after. (For me, personally, I would prabably do it before the move.) One reason is that when the girls are potty trained, they are going to need to be able to get out of their beds, and the other reason is to make it so much easier for Mom to put them in and get them out of bed. Plus, if mom and dad are having a moving sale, they can sell one crib and not have to move it! (Keep one for the new baby, of course.) :)
The potty training can actually wait until they are closer to 3, but you and the parents need to be aware of the girls' clues that they are actually ready to potty train. If their mom already has them, you (collectively) can go ahead and introduce them to the potty chairs. Our son "played" (sitting and flushing) with his potty chair for around 6 months before we actually moved it into the bathroom for actual "use". We also bought a Play-a-Sound "Potty Time with Elmo" book for our little boy when he was around 18 months old. It's one of his favorite books, and he very often finds it to take into the bathroom with him when he's sitting on his potty. (The book is not gender specific, so it's great for both boys and girls!) We got ours at Babies R Us.
Hope all this info helps you guys! Good Luck, and please tell Mom and Dad "Congratulations on the new baby!"
~J.~