@AshevelendarShow me your faction and I shall think about it. For now, anything goes...within reason of course.
@GenniA bunch of gang members need to explain why suddenly they all died? They are Raiders after all, not Brotherhood.
Kill-all means KILL ALL. No matter if they were Synth or otherwise - plus, if your bunch is a band of raiders. It might have been a VERY big stretch on why you have as much synths in your ranks as they are. Since the Institute wouldn't see much reason on replacing several members in a single gang.
Also, as I've said - you'd be much easier having your gang be formed from escaped Institute Synths of the Brotherhood attack. Since that breaks less lore.