How many sisters does Spencer Pratt have?

In previous episodes he once said to Heidi when shopping for a dress"I know what girls are like I've got two sisters"and in the playmate episode he says to one of them"my sisters"(plural!)I'm confused because apparently Stephanie's his only sisterAnswer please!

he's pretty much just an idiot. but it is possible that he has another sister who doesn't want to be included in the hills (who could blame her?) so the producers just pretend she doesn't exist.