Jim, you can ask for 'right of first refusal'. It means that if she can't be with the kids, you would get the option to take them. This is standard.

M 16 yrs, WH62, P54
3 adult blended kids
EA 11/13, BD1 6/14
PA fall 14, BD2 2/15
Piecing 2015, BD3 12/15
Separated 4/16
WH moved OW in 5/16
Divorced 6/15/17