accurate mouse broadcasting really requires all the windows to have the same aspect/resolution (delete as appropriate, i'm not sure), Keyclone from experience wasn't ideal in this aspect.

You could try tanking using focus and selecting the actual target for your heals, so your macros would be something like
/assist tank
/heal

Then your tank would have his/her tanking buttons have /cast [target=focus] (Someone here can correct my grammar)