Hidnsight being what it is, your DH should have objected to the move.
while you line things up for attorneys and court, start documenting everything. DH needs to send her certified mail requesting his visitation at x time. If she does not give you a response he will need to go and attempt to get the children. When she refuses file a police report. You will need PROOF of denied visitation, his word becomes just that he said she said.
Also start keeping copies of Phone records and look into recording conversations. Make sure when you record you record from dial tone to dial tone. This way you are covered and you catch the numbers tones on the tape to prove who you called.