Hey. I can't help with your first question, but I can with the second. I have fraternal boy twins. And I agree, they are just lovely.
. For PU/PD and for naps, I've found it's best to do one at a time (jiggling two babies at the same time seems to make mine more mad). I have a wind down for them each individually. So I'll put one down like ten minutes before the other(you'll want more time initially since you are training them), usually the more volatile one and the other is fairly content to play for a couple minutes by himself if the crying one is not nearby. So I hold them vertical with their head above my shoulder and do the shoosh pat until they seem content(oh five to ten minutes) then lay them down. They usually wiggle a little then fall asleep. Sometimes if they are overtired I do this several times. Make sure your pats are rhythmic and gradually get softer. Works miracles. Then I get the other and do the same thing for him. I think the key is to not let them feed off of each other's possible.
Is it possible to get help putting them down for naps just while you are training, or at least until you get down the timing? I think that would be very helpful if you can.