My MIL(U.S.Citizen)had filed for her bro's family for their GC(bro,wife,two children)in 1998.At that time,the children were below 21 yrs of age.Now,her brother has got letter from USCIS for their family to immigrate to the US minus their children, since the children are 24 and 25 years of age now and are unmarried.Based on CSPA law calc,the two children still qualify for the immigrant visa.The primary beneficiary is planning to enter along with his family sometime in the next two months or so.
1)When can the petition be filed for the children?Do the primary beneficiary has to enter US,get his GC and then file it or do they have the option of filing it from their home country even before they arrive in US?
2)For filling I-864 form,should my MIL incl or exclu children?