If I may, praise the lord for all of your efforts. My kiddo has some a few of the dx's you mentioned and he is a handful and half all by himself. You must be exhausted!
I wish I had a magical cure all for you, but sadly all I have is something you are probably already doing: praise and reward for staying in their seat for a few minutes at a time and then slowly build stamina. I use a watchminder (purchased by my district behaviorist at district expense-you might as well ask what the worst they will say..no) set to alert me and remind me to "reinforce good behavior" every 5 minutes when its really getting tricky, then I up it to 7 minutes, then 10 and so on. If they can be successful at 5, go down to 3 minutes for the first 2 or 3 work period of the day then take it off or you will go crazy being interrupted to reinforce behavior so often and if you need a 3/1 reinforcement schedule (once every 3 minutes) setting small goals like for 2 or 3 work period per day might be more reasonable and progress is progress even if its slow and only for 1/3 of the day. The first 2 weeks is extra exhausting and feels unsustainable but then it get easier because they start to make a little progress with any luck and you dont have to sustain such intense frequency.
Also, and you may also already be doing this, I would give little to no feedback when these students get up and walk over to you. I would tell them in advance that the procedure is to 1. Read the directions, 2. try to get started, 3. If they are not sure what to do ask a neighbor to make sure they understand, 4. skip to an easier problem/question and come back to harder ones later, and 5-raise your hand for help if you have tried 1-4 and cant get started BUT know that you might have to wait a minute. I would type up the procedure with pictorials and attach it to their work area and then if they tried to come over to me and not follow the procedure I would point them back to their seat without talking to them or making eye contact and if they didnt get the hint after a minutes or 2 of wordless averted gaze pointing I would say and repeat 1 word: Procedure/checklist/seat whichever one I felt they would understand best.
Best wishes and prayers for strength...and perhaps a couple of glasses of wine at the end of the day.
