One of the FAQ’s & concerns approximately the Sims ar is the family limit v Pets. Now we have actually our answer shown via 
Gamescom 2011.

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The Sims 3 Pets growth has bumped the household limit by 2 totaling 10 members. This method you can mix and also match between 8 Sims and 6 pet that execute not exceed 10. Pets will count as member of the household and also take up a spot.

Note that just Playable pets (Dogs, horses & Cats) take it up a clues in a household panel. Lizards, Birds and other collectible pets can be got by the dozens. (assuming you have enough money)