The kids are probably reacting in a variety of ways - individually, based on their age and emotional profile. It sounds like you are doing a really good job with them.

A practical suggestion - can you turn on video chat with WH so the boys can see her and she can see them? If you do, they may come over to the phone.

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