Sounds brilliant, guess its not surprising not everyone wants to take part, its a big step. hope your sister comes round. its hard to bring up stuff and talk about it, so there may be a lot behind her reasons...
I'm not entirely sure re how you access it... would you be happy to go through your current care team eg your GP? or if you're under a community team, they would be able to refer you for family therapy. there will be waiting lists I guess, but even if they can't see you, they may be able to point you in the right direction.
Or your previous therapist may be a good resource, I've heard you can self refer to CBT like things through IAPT (not sure what it stands for!) so that might be worth googling for your area.
Also wondering if they can do it over the phone or skype if distance is an issue. though being in the same room helps doesn't it.
There may be some pointers on the association of family therapists http://www.aft.org.uk/consider/view/consider.html
I just found this too which looks interesting, if you can all get into London http://www.ift.org.uk/counselling-therapy-services/