The other fish in the tank are Cyphotilapia frontosa (big fish) and looks like Neolamprologus tretocephalus (small fish). However, the small fish could be baby frontosa but I think they are tretocephalus.
They are from Lake Tanganyika and require water with a pH above 8.0 and a GH above 350ppm. Whereas the Jack Dempsey is from Central America and requires water with a pH around 7.0 and a GH below 200ppm.