We need to know the size of the tank to answer this correctly.
If the tank is big enough and the firemouths aren't small enough to fit in the senegals mouth then I don't see a problem. Tank size is important though synodontis and cichlids are territorial and could give each other a hard time is there is not enough space.
Personally with the fish you already have I wouldn't risk it in anything under 5 foot.