You don't have to go from helping them get to sleep to nothing if you don't want to. I also don't have experience of toddler twins, my twins are only 5wks, but my first child was a complete nightmare - mainly because I never taught him to settle himself to sleep at the start. I've always been against any form of control crying, so we had him in our bed and I fed him far too much in the night. We got to somewhere over a year when we just couldn't cope any longer pacing the floorboards rocking him to sleep every night and several times in the night. So god knows how you're managing with two not sleeping well, well done for coping this long.
I got some common sense advice and support off the lovely nursery nurse that worked at our local health centre. She suggest that if we didn't want to leave him to cry then we had to work on gradually removing the props that we used to get him to sleep, it would take longer and it would involve some crying but we didn't have to dump him in his room and shut the door.
We got him a new bed(2nd hand) and put him in his own room, then NN suggested spending some time over a week or two playing in there to get him used to it, then once he was to start sleeping in there laying down beside him at bed time to give him the reassurance to go to sleep, when he was ok with that to then put a chair by his bed and hold his hand, next stage to drop the hand holding, next moving chair away from bed, next waiting out side room giving vocal reassurance, then final stage putting him in bed going through usual routine, story, song, kiss goodnight, then leave room and go downstairs, but returning to give reassurance when needed.
This wasn't easy, but it did work eventually, we missed out the laying down next to him bit and thought new room, new start we'll see what he can manage, he only took a few days to accept that I wasn't going to rock him or lay down next to him. There was tears at each stage, but I felt that we never abandoned him to do it alone.
Having never taught him early on to sleep well he's now 2.5yrs and still not a good sleeper, any change to his routine ie vistors, illness, or a missed nap the day before can mean we have a bad night. We've also found that if we go to him in the night now to settle him when he wakes it means he will wake more that night and the next night. The more we go to settle him the more he wakes - so sadly the only thing that seems to stop him waking more is leaving him to cry. It breaks my heart every time. Sorry about adding the gloomy bit on at the end after telling you there is hope - I just wanted you to be aware that once you get your twins sleeping through that it might not mean it's plain sailing from there on in.
I really hope that you are able to find a solution that you feel comfortable with. You might be able to get some good advice from your health centre. Hope you have some peaceful nights soon.