For the heroes, when a player gets near and is "selected" you can probably make it unselected somehow, which makes it so they can't buy.
For the fountain just do when a unit enters in a range of 400 near the fountain, have create a dummy unit which casts a channeling heal spell, when they leave the 400 range stop the channeling and remove the dummy unit.
No, one of the things you can do is the example I gave in my comment.
OR You could have a fountain of life which is "friends" with team 1, and set healing ability it has to only affect "friends". Same thing goes for team 2.
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.