Hmm...been doing some research and it might not be true, but that's mostly from shelter sites who almost always advise you to spay your pets regardless. Looks like opinion is divided to be honest. In fact, I've just found this interesting article: http://www.angryvet.com/spaying-and-neutering/ Sorry, I like to research :D
Thanks! It sounds like you're being very responsible with them which is great to see! Hope everything goes well with them :-)