thankyou for writing this mandamoo 42, it was just like i was reading one part of my own life, only my stepfather was doing the same as my brother, brother caught me every time as i passed his room, and stepfather would come sneeking into my room or grope me whenever I got in reach of his grubby hands. yep I was a wreck. yep mother knew, and like yours she let them stay and continue because 'I would leave home in a few years time and she didn't want to grow old alone' She has made me out to be a liar too. only my patience has paid off, i heard last year that the arsehole(stepfather) died after getting a horrible skin condition, so now she is alone...justice for ignoring my needs.
I decided the best way for me to deal with the past was to stay there just long enough to get my grades at colledge, once i had them i was equipped to financially support myself in work, i moved 200 miles away and kept my distance, they never cared so neither did i for them. i think of the whole family as pieces of shxt. I did crack when i lost my partner but even then mother was more interested in herself than my needs. that concreted my thoughts that I have no family, to me the whole lot are dead. I have had a life mixed with all sorts of feelings, some good, some bad, and yes i am under mental health because of my childhood experiences, but I am still better off without my so called family than i ever would be by including them in my life.
I have accepted Mother will never understand what her denial has done to me, or how much i crave for her to love me, but know this will never be.
As i was told many times as a child I want doesn't get.

on a positive note, if your GP will not refer you for talking therapy, have you thought about contacting PALS (patient advice leasion service) they are pretty good, other ways are to contact your local MP councillor or the corperate complaints manager at your local council, they are usually pretty good at helping put complaints together and sorting things out around health issues.
good luck x