I'm 61 retired my wife is 62 works part time we just adopted one grand child shes 2 and will be abopting her brother in jan hes 4 she was in state custody he is not. Can they get ssi there mother is on ssi.
When you refer to SSI, I don't know whether you mean Supplemental Security Income or Social Security Insurance. Supplemental Security Income is a needs based benefit that's paid only to the eligible individual. There are no auxiliary benefits paid to the children of an individual receiving Supplemental Security Income, unless the children themselves qualify for Supplemental Security Income.
However, if the mother of your grandchildren is receiving Social Security disability benefits (SSDI), her children may be eligible for benefits on her record. If so, their subsequent adoption by you wouldn't terminate their benefit entitlement. You should probably check with Social Security to see if the children qualify for benefits.
I should also mention that your adopted grandchildren will likely qualify for child benefits if and when you or your wife start receiving Social Security retirement benefits. That could affect your optimal filing strategy, so you may want to use the maximization software available on this website in order to determine your best course of action.