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. 8 o. G8 l% Q. V$ }+ d* H5 T 3 X2 @; @& z9 l/ z! y, w6 g/ ~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.