Afraid of little dogs!

[AerynAerie]

My almost 11 week-old pup is really scared of the two small dogs next door (miniature chihuahuas) and my Aunt's Miniature Pinscher. Everytime he sees/hears them he tucks tail and runs away to hide.
He's good with my mom's dogs (miniature pinschers) who we see every weekend. They often play chase and tug with toys and lay around together.

How can I get him to be braver around the other ones??
He's not afraid of big dogs at all, just the little yelping ones.

Also, he's afraid of lawnmowers...I don't own one so I'm at a loss as to how to desensitize him to that sound.