i did the same thing for my uncle and aunt. i don't know if it is ok.but i called the telephone number which was on the letter, asked them to add the dependant, it costed me 18 $ to call them. if u want , u can call them.
tttjjj2002, thanks a lot for your info. 0 L( M: `* ?, Z; w0 X; j0 T& z3 u5 W
Anyway I am not in a hurry, so I gonna take risk, go thre to try. If they refuse to process their application together, then I'll make another appointment.