My bro has his house built in the rural Kentucky, and they've subdivided out
his Holler into a few parcels where the families live. Let's say three
structures: Bro's house---200 feet, S-I-L's house 100 more feet B-I-L's

He wants his wireless to extend to the BILs house (it reaches but the signal
is weak). I was thinking I could put a router (maybe an airport express) at
the SILs house, add it to my BRO's network and then the BIL could connect to
it since it's much closer. The router doesn't have upgradeable anntenae.

I'm open to buying new hardware too. Anything you got in your brains more
clever than me?