connected with the relationship that exists between people or groups that share the same ideas or interests (Oxford)
connected with the relationship that exists between brothers (Oxford)
relating to brothers (Cambridge)
friendly, like brothers (Cambridge)
of, relating to, or involving brothers (merriam-webster)
He’s a member of a fraternal order/organization. (Cambridge)
The idea of fraternal correction was discussed in conciliar disputes. (Cambridge)
There was a fraternal feeling among the troops. (merriam-webster)
fraternal order/organization
fraternal correction
fraternal feeling
Congenial
Friendly
Incompatible
Unfriendly
Fraternally