I feel your pain! (and joy!) We have 2 year old twins as well as a 5 year old, 3 1/2 year old and a 4 month old...I just took the twins out of their cribs and we actually took the leap to put ALL 4 girls into a King size bed. I did this for a few reasons. I had moved my 3 1/2 year old straight into a twin bed with her big sister at that age and found it (after some major adjusting and consistency) to be a great move. They have each other for company and bonding, they learn to sleep with another person and become less noise and movement sensitive and learn the lovely art of self control and obedience to what mama and papa say regarding bedtime. :)
First off, I had to give up their nap because they won't fall out on their own anymore until 10 or 11 pm if they nap in the afternoon. This has probably been the toughest part because they get so sleepy around 4 pm and by then it is too late to lay them down. Our solution has been a quiet time in the early afternoon where they need to sit on the couch and we all do silent reading or practice listening skills and then in the afternoon before dinner (my least favorite part of the day, everyone gets so grouchy) we try to be on a walk or at the park or just outside playing. This seems to get them through the hardest part of the day nap-free :), usually.
With the twins joining the bed now we have had some issues (not surprising) with them talking, playing, crawling onto other girls who are trying to go to sleep, tickle wars, hurting each other, sneaking to get books, etc...
Our response has been to be very gentle but VERY firm about when we say the playtime is finished and they need to lay on their own pillow they must obey. I try to keep a routine before bedtime that allows for tickling, lots of reading, singing, jumping on the bed, etc. That way when I have them change into pj's, brush teeth, potty, drink, lay on their pillows, turn the lights off and sing softer songs they know it is time to settle. We also value our evening time but we value our kiddos learning to obey and settle in as well. Right now we typically have to stay in and snuggle longer with each twin plus the older girls and sing them each one song softly while gently helping them lay back down on their pillow. As you can imagine, this takes a lot of time. Our bedtime often takes an hour or 2. This is not going to be forever. I view our time spent in their room at the beginning of these transitions as an investment in the future happiness and peace for our girls learning how to fall asleep. Also it is our family time and we love it. We try to leave the room before they are all the way sleeping and often have to go back in as someone sneaks out or starts talking again. But again, training them young reaps HUGE rewards for the coming years. It's like early potty training. People assume it is too hard and children are too young but I have found that consistent efforts on the part of parents earlier make for MUCH easier older years and less work in the long run (think of how many years of diapers I have not had to change because I did the hard work of toilet training young.)
I guess what I am encouraging you with is that you CAN make these transitions but it won't be simple or fast! Not much that is worth having is! :) There are lots of tricks and ways to manipulate good behavior from our kids but I think much of it simply boils down to kids needing to trust the authority of their parents and obeying directions. If we are authorities who are truly kind and not just selfish, they will learn to trust us and to respond to our authority by honoring and obeying. Then we will not have to manipulate, threaten, reward etc. It's all about loving and obeying. :)
My best to you in this crazy journey of parenting multiples!!!
Cheers,
J.