I don't think it's a stupid question at all. I've never kept multiple Firefish in one tank, have heard as TheShrimpNibbler mentioned that they will kill each other off over time. I have a 140g and have a Green/yellow Fang Blenny and a Bicolor Blenny in my tank with no problems. Also have a YWG, a Sleeper Goby and Jawfish, so far no problems with any of them clashing but you never know over time. If you try to keep multiple Blennies try and avoid getting similar looking Blennies, they will fight with a fish that looks similar to them. For example you have a Midas Blenny so I'd avoid say a Yellow Fang Blenny as most likely you'd have problems.