Hi there and thank you for your question,
I don't think that there is any obligation on you to send the kids to the father. Make the necessary plans and see what you can do that is best for the kids.
Then, if the father is upset about the decision, then let him come to court to ask the court to make the kids stay with him. He will need to show that it would be in the kids best interests to do what he wants, and not what the mom/you guys want.
You should carry on as per normal.
If the dad can't financially afford to look after the kids, then why should he be entitled to complain when you guys are doing your best and he doesn't like that?
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Good luck and best regards,
Please note: This answer does not create an attorney-client relationship. Please consult a local attorney in person for legal advice. This information is being provided so you can better discuss legal matters with your attorney.