Can a peruvian mother-resides in peru,gain citizenship for her half american baby without the father knowing?

My brother is US citizen by birth, DNA tests and a hefty child support established/positive through the american embassy in peru. They were never married and he has never seen his 5 yr old son. He wants to see his child but he was told he has to file for joint custody through the peruvian courts to have any rights. Is this really fair? She says she cant come to the USA without the "father giving his name legally" to apply for a passport, so she says, is this true or does she have alterior means like filing for citizenship without him knowing? My brother won't sign anything untill he can have at least joint custody or sole custody and his child lives with him in the USA (VA) Are there any rights for fathers?