I don't think the physics of balancing a rocket on the way down are any different from doing it on the way up. I'm also not sure where you got the idea that us

I don't think the physics of balancing a rocket on the way down are any different from doing it on the way up. I'm also not sure where you got the idea that using multiple boosters is a problem. Look up the Atlas 5, Delta IV Heavy, the Space Shuttle, Ariane 5, etc, etc. (And multiple engines on the same booster have been used since the start of the space program.)