I will start to apply my US citizenship soon. My question is: as a US citizen, if I apply for my sisters' (family 4th category) GC and they are in US already as tourists (B1 visa is gonna expire in one year), do they (and their family) allow to stay in US legally until GC is approved? I know it will take more than 10 years to get approved. So they won't leave US in 10 years for sure if they can stay legally. Any advice/information links are highly appreciated.