Isaiah needs to play off the ball more; he is holding onto the ball so much the offensive rhythm is broken. I would start Brown and play him against Lebron with no switch just help in the paint.
The physical tone set by primarily by Smart and Brown looked to spark the few runs tonight. If that tone is set early on Friday, the game will be a lot closer. So I would consider bringing Smart in earlier.
As for defensive rebounding, crash the boards and limit going for blocks. This weakness isn't going away; the team needs to overcome by winning more 50/50 balls.
On offense, get into the paint. Stop shooting threes early in shot clock. Only shoot threes off drive and kicks or offensive rebounds; otherwise, get into the paint and draw fouls. Also, Isaiah stop holding the ball; instead he should be coming off picks without the ball and, then driving into the paint while the Cavs try to recover, so more players are open for cuts and corner threes.
As the saying goes: good offense leads to good defense. So our offense can keep us in the game by limiting the transition offense for the Cavs. Less switching will prevent the easy mismatches at the 1,3, and 4. Isaiah shouldn't switch onto Lebron or Thompson and Horford shouldn't switch off Thompson or Love to pick up Lebron. If we can limit those easy bucket scenarios, they aren't going to score nearly as much.