Crumbs, missdisorganised. I haven't read all your posts on other threads, but I just wanted to say that I think you are incredible to cope with all of this.
It sounds as if the Deputy Head is very supportive, so can you speak to them about the Forum Tutor's constant gaffes? He has the interpersonal skills of a socially inept skunk at present - whenever he has to mention your situation or your parents he just lets off a stinker.
Can you ask the school for a "mentor" - possibly a member of staff with experience of bereavement, or a younger member of staff who you can really relate to? Someone you can turn to when it all gets a bit much during the day for whatever reason. I hate the idea of you having to go to the toilets to cry alone.
I think that you will find that there will be support at Uni - in fact probably more than there is at school and more readily available. Most Unis have part-time or even full time counsellors, and most will have a medical centre. They are there for a reason, which is that students leaving home for the first time need a lot of support. When you first arrive you should get handbooks/directories from the Student Union and the Uni and they should contain everything you need to know about support services. (All online these days, of course, not like when I was a girl.)
It would be worth contacting the Head of Department beforehand to tell them about your situation and to ask for a Personal Tutor who you will be able to support you. You should get one anyway, but you will need one more than most and it needs to be the right person.
I am going to read your other posts and watch out for new ones. Keep your chin up and I really hope you get the grades for Uni, or an allowance for them if not.
Sending you a very big hug.