Again, I'm not an expert on this but I don't think that's true.
Once they're on the board the only way they can be removed is if:
A) They resign
B) The other board members by a majority vote them off.
This is one of the many reasons it's imperative to stop Kroenke gaining sole ownership of the club and why despite how horrible he is, it's vital that Usmanov retains his share of the club.
Bibbles can perhaps shed further light on this, but this is exactly how Hicks & Gillett got screwed over at Liverpool despite being majority shareholders.
If the rest of the board members had any spine they could collectively between them isolate Kroenke and actually instigate some major changes at the club. Clearly they don't.