I can't see the authorities stopping a criminal getting into this country - can you? Look what kind of people are allowed in right now. And once here, they seem to be able to stay. I think you are in danger of having your in-laws' problems offloaded onto you. If it were me I would not want to have the nephew over and neither would I pay for anyone - you may have to be responsible for them whilst they are here. This is a time to be tough because once they are here you will probably find it much harder to be tough.