I have a Hg repo with 3 branches in it, but two of them are inactive (since I have already merged them into my default branch). hg heads shows 3 heads, one for each bra
To push a single branch you just use -b
hg push -b myBranch
as for the specific issue, you may want to look into closing branches. I know SourceTree offers it, but I'm not sure on the specifics