Non -accompanying dependent children

[mrrm03]

Im sponsoring my spouse he have 2 dependent children apparently with different mother.. The other one refused to have her child a medical examination is it acceptable to have a refusal letter signed by her and notarized?? Or does my husband need to go to judge for the custody.. He's been a good father to them and keep financial support eversince.. Is this gonna make my spouse application delayed or denied? If thats the case Can we just not include the kid with uncooperative mother.. I want the kids to have an option in the future but with the uncooperative mother what should we do?? I didnt know its gonna complicated since my spouse not been married but support he's children financially..