I will race you going poop

We are in potty training madness around here.  With four children, still requiring diapers full time we continue to have the hope/dream/desire that one day they will be toilet trained.  These four children have a variety of significant special needs and it has been thought by their medical team that they may never be able to be toilet trained.  I am encouraged by the fact that 2 of their brothers with similar challenges were successfully toilet trained, during the day, by the ages of 5 and 7 years.

There is a lot of literature available focusing on toilet training and there seems to be a general consensus that if your child exhibits these signs they are ready for toilet training.

Is your child aware of the difference between being wet and being dry? That's a NO times four here.
Can he stay dry for at least 2 hours at a time? One can but due to medical issues, not bladder control.
Is he capable of reaching the toilet or potty in time? (Perhaps with our help).  That's a yes with help.
Can he undress and dress himself or is he ready to learn? This is a skill that we have been working on with these four and it seems the youngest of the group is the most successful at dressing, in a limited way.
Is he motivated at some level to take this next step?  I really don't feel that these four are motivated to be toilet trained but they are motivated to sit on the potty because it looks like a fun thing to do especially when a sibling is doing this.

There are many thoughts on how to train your child and having tried multiple methods, we have narrowed down to a method that is manageable for us.  The children sit on the potty when getting up in the morning, when getting ready for a bath and when getting ready for bed.  My 2 1/2 year old shadow, is only allowed to follow me into the bathroom, if he sits on his potty while I am in there.  We use this method ongoing even when we aren't "actively" potty training.  Our thought is that the children will learn the motions and become comfortable with what is involved in using a toilet.  While following this plan they are dealing with many sensory and balance issues on top of the toileting issues.

Every 4-6 weeks we "actively" work on potty training for 2-3 days - armed with big boy/girl underwear, multiple changes of clothing, cleaning supplies, a carpet cleaner and hopefully enough patience to survive the next few days.  If this stage produces even the slightest glimmer of hope we continue, if not we resort to the more laid back approach and diapers.

This go round the 5 and 8 year old are both very hopeful that their bodies will give the desired results.  They will sit for hours, next to each other on the potties if you let them, chatting away.  While sitting last night one said to the other "I will race you going poop"  the other eagerly accepted the challenge unfortunately neither have the muscle control required to complete the race (both are medicated to have bowel movements).  The positive sign is that they know why they are sitting there and we will continue praying they can eventually become toilet trained.