hi girlymom2. I'm sorry to tell you that I never figured it out
they eventually started to die out... but it took months.
I did find an old storm drain outside my bathroom that was so covered with dead leaves that I had never seen it before! I found it because I had to rip up and replace every single storm drain outside my house
I don't know if that was the cause of the initial problem or not. Maybe it would be worthwhile for you guys to put a garden hose down all your exterior drains in case they are breeding in there.
I know its really gross looking but fly paper helped a lot. I also kept a bottle of rubbing alcohol in a spray bottle in every room and one small squirt was enough to kill them and I didn't have to use nasty bug spray.
Best of luck. Hang in there! I know how frustrating and annoying those things can be!