It appears that you do have 2 different clownfish species in there. 1 is a Percula ( usually described as an ocellaris with black borders around the stripes) and the other appears to be a Black variation of a saddleback clown ( A. polymnus) which, when juvenile, appear like a percula/ocellaris and were sold under the common name "Black Percula" back in the day. With all the tank raised clowns now out, they may have given this fish a new common name.
If you look at the pics here ( https://www.fishbase.se/photos/thumb...ecies=polymnus
) you will see a number of color variations for the polymnus based on location. I suspect it also has to do with the anemone it attaches itself to at these different locations.
As for compatibility, as singles, there is a chance, if the tank is large enough, for the 2 fish to get along as long as they can get out of each other's way. If you add a second member of either specie, because of their ability to change sex, you will eventually wind up with a male/female pair of that fish and will most likely kill off the stranger. This is based on wild fish habits. Tank raising these fish may have altered their natural instincts but it's a gamble to assume that has happened.
Hope this helps.