Mama I had SPD with J and found the pain unbearable at times. I used the lift to go up & down 1 floor at work
but it really helped - living in a bunglaow helped too.
Thanks for the support everyone. I text DSis last night as I had wound myself up about it (again..).
Upshot is: He is back as he 'wants' to stop drinking and be near his family (but not his step son...). DSis has told him that she won't have her DS1 back until he has been sober for a year (that was my rule / suggestion to our parents as it's just too cyclical with him not drinking, C going home, he starts drinking, C has to escape...). So I am glad she has taken my rule onboard.
My personal recommendation is that he stays with his Mum, she drops the kids off for 1 day at the weekend, picks them up and that's all there is contact -wise until the year of sobriety is up. Sadly, she started to do this but then she started 'talking' with him, then he came home to look after the kids during the holidays (he's on disability as he now has Chrones - forgive me for sounding nasty but when I first heard this my initial reaction (and secret wish) was - hopefully it'll kill him). Because he has been around so much they are very much back together - although she claims to not like him and thinks he's a prat... Hang on - so WHY are you still with him?!!! 
I moaned about never seeing the other 2 children and her never seeing J. She has promised to come 'round every week - I was like 'yeah, won't hold my breath'. But she has arranged to come tomorrow after collecting the other 2 from school and take them & J to a play park down the road. I have no doubts that she will. I just want her to see the madness of it all. That none of her family go to her house because of that waste of oxygen she married!!!
I reiterated that he is NOT her responsibility but her son is. Get rid of him (forever) and have her son back. So simple to a sane outsider, so difficult for a mentally abused woman.
She is so lovely too, she's gorgeous and fun, a million times prettier and 3 stone lighter than me. Yet I am the one with the 'perfect life' and she's had nothing but drama.... Wish I could swap places with her - 10 mins and the whole lot would be sorted out!!!
And relax... 