I completely understand your problem. It is very difficult to cope with
the loss of a parent, but you have to pull through. I know your dad and
big sis are hardly around so what you are missing is the adult around.
What you should do is try to connect with the members of your extended
family counsins, aunties, uncles, or even your grandfolkes. Because
friends are not your problem you need to bond with your family maybe it
is you who has to do the reaching out. Hang with your family and try to
make the best of the little time you have with your dad.
I do agree with Teeniebopper.Don't loose hope.Be brave.Try always to be
in touch with ur dad and sister.Try to make the best time with ur dad
and be in touch with ur sister through mail.Even if she doesn't reply
keep on mailing.Someday she will realise it that u too need a some to
take care of.Be happy and try to spread it.