Hi Munkee, i think you have almost a surfeit of advice here, some of it very good and some of it really not so helpful (polite description).
I would suggest that you keep schtum with your current tenancy, don't let on that you're not intending to just walk out the door as soon as they ask. Keep your rights going as long as possible, at least until you've made a decision about what you want to do next.
I would personally "advise" against moving in with your Mum. Being a carer is a 24/7 "job", 365 days a year. In theory you can get some respite care, in practice it's nothing like as much as you'd need.
I would suggest you ask ALL the various agencies/groups/etc you can get hold of, about your rights of tenancy if you do move in with your mother. They will all advise according to their own preferences/requirements, and not all are known for their truthful answers. Meanwhile some can be entirely truthful, yet over time the rules change beyond their control.
I would suggest that you think about other ways you might be able to help your mother. She will almost undoubtedly come to need a full time carer, and if you are doing that you simply won't be able to cheer and amuse her as you and she might like. You might be better placed as a cheerer than a carer.
I think you really need to think hard about what it is you'd like to do. You mention involvement with children, which is less likely to happen if you're totally exhausted by caring for someone who right now "refuses" to move to accommodation that would be easier for her to live in, and as time goes by she's likely to become less amenable.
So you could probably help her more by spending a little less time with her.
Remember that old phrase, "possession is nine tenths of the law". It's also a good negotiating tool. If you work out what it is you want, you might be able to negotiate those: eg if the council want their 3-bed property back they might swap for warden controlled for your mother and a one-bed flat for you. (worth a try)
The last time I looked into it, if someone (relative) had been a live-in carer for sufficient time they could negotiate a proper tenancy on the death/moving to care-home of the cared-for person. As others have said, varies from one council to another, but reliable info prob best from eg CAB. EG the council won't tell you the loophole if they think they can move you on.