2 nonEU students,one goes dependant,8 n 6 yrs, any advice

we are two nonEU students, i m here 8 she s 6 yrs, we are not living together yet but trying to arrange it.

i do know roughly the procedure: we need COAs, designated registers, and then i have to apply for some dependant status?

which form do i use to apply for a dependant extension?

what r the usual problems with it? any advice to us.

will the home office get prejudiced about my nearing the 10 yrs mark, i have been in UK for 8 yrs?

has anybody had/heard funny cases when all docs seem to b ok but IND still refuses. Because i have heard about such a case, though i dont know the particulars unfortunately.

i would very much appreciate anybody's help
thank you
m