as well as whether they live with you and whether they make more or less than $4200,
do they files taxes and claim the children? are they married to each other?
I don't think they are filing taxes this year. Income is below $4,200. They are not married. They live in a separate home in another local town that is in our son's fiance's name and our name, that we pay the mortgage on.
It is not likely that you can claim any of them. They must have lived with you for the entire year in order to claim them as qualifying relatives.
If they lived with you for all of 2019, you provide more than half of their support, and they had income of less than $4,200, it is possible that you can claim them as a dependent (qualifying relative).
Rules for Claiming a Dependent