Wow, they are lucky to have found you!! I'd be careful who you give them to. Be positive they are the real owners. If they lie to get a free dog you might not want the dog in their hands. And what if the real owners show up later. And like someone else said I'd give them all flea baths and carefully pick off the ticks. Let us know what happens, and ya know... if you don't find their owners... you may just have yourself 3 more Yorkies!!
But rescue groups are great and I'm sure if you decide to you could find them awesome homes on YT! Good luck!