We got physical custody of my husbands two children in march.. she was supposed to get them in march for spring break and then the month of July.. she gets two visitations a year.. by the time her next visitation comes around it will have been a year and a half since she seen the kids or tried to get in contact with them.. how long does she have to got without seeing the kids before we can file abandonment?

Contrary to common belief, you do not 'file abandonment'
Abandonment is a criminal charge that states the parent or caregiver left the child(ren) unattended, and alone for an extended period.

They were left in you and your husbands care. That is not abandonment.

You need to contact the courts to inform them that the children's mother is not keeping up her end of the visitation. Keep records of EVERYTHING.

As noted you can't "file" abandonment.

Nor can you force a parent to be a parent.

Please read this sticky:https://www.askmehelpdesk.com/family-law/child-abandonment-read-first-364259.html

Then come back and tell us what you really want.