It won't be easy for them to find care for all 4 at one home. You do have the perfect situation if you can only take them for the summer. Just be sure they are not assuming you will be available for before/after school care.

The problem I find with people moving is that they contact you in a panic and say they will accept whatever your terms are but then once they get moved and settled they learn other things like the lady across the street does daycare, or there is a great camp the new friend next door is going to.