How many cats are too many?? (Updated 1/18)

2012:  The Queen (top) and the Princess 

ORMOND BEACH, FL - - I've noted before that we miss the two furry kids who were our companions for 17 years.  On the other hand my brother (in upstate NY) now needs a calculator to keep track of his tribe.
      It all started about two years ago with his regular feeding of stray cats (and birds and squirrels, etc.) on the back deck of his house. Eventually, he took pity on one of the friendlier cats and she repaid the kindness with five kittens.  So, one by one, my brother had the five spayed or neutered...and of course they moved in.
     So that they could go in and out at will without waking him in the middle of the night he installed a pet door in the garage downstairs.  This Fall, he installed another pet door...this time so they can get into the house for food and water and warmth.  He has called me numerous times to note he is sitting on the couch with five growing feline buddies.  I've mentioned to him that pet doors could prove troublesome.
     This evening (Thurs.) I got a call:  "I got up this morning and counted heads and tails like I usually do" he told me.  "I want to make sure we haven't lost anyone to the raccoons or coyotes.  Not only did I not lose anybody, but I gained two!  Now I've got seven instead of five.  It seems the gang of five 'taught' the other two how to climb through the pet doors."
     I was waiting for the next line:  "Are you sure you wouldn't like a couple."   
     UPDATE:   Friday evening (1/18) we got another call, "Guess what," said my brother.  "Now there are 9 cats.  They all get along although I think it's more because it's cold and snowing than because they like each other."
      Any bets on what the next population build up will be?  The weather forecast notes there might be as much as 12 inches of snow by late Sunday.