C.,
Have you tried some sort of reward system? I had to give stickers each night to my then 2 1/2 year old for her to sleep all night long in her bed. After 4 stickers she got some sort of reward. Then the number of stickers increased. She's ten now and never wakes me. :-)
Also, you guys have given up after 117 tmes before, right? Well, your kids know that so they may even try 127 times the next night. Creating a habit is easy but breaking it is exhausting. (I've helped created several undesirable habits during the course of raising my kids)
If your goal is for your twins to go to sleep without mom and dad in the room then stick with your plan.
Would a checklist of some sort work to get them ready for bed. Are they visual learners? Make a picture chart of what to expect at bedtime (put on pjs, brush teeth, read nighttime book, hugs from mom and dad, lights out, go to sleep). Depending on age is how many things you list. (for example, a two/three year old may be able to handle a system of pictures where you have two spots: first we do this and then we do this. You move the pictures or let the children move the pictures when task is completed)
Also, would it be possible to seperate them at bedtime. Do you have another room? I am sure they feed off of one another. Could you put the heavier sleeper to bed first? I had to do this when I had all three of my children in the same room.
Here's another idea - if what they want is snuggles from mom or dad could you set a timer of how long you will lie down with them and when that goes off you have to leave the room? I don't know if that would work....
Good luck! You are doing a great job. Just stay consistent with not sleeping in the room with them if this is the goal you are hoping for. (I have been there sleeping on the floor of my child's room. I know it is no fun and eventually we worked it out and all three of my kiddos sleep like champs.
J.