Parish has as much say as the other owners, he's just chairman aswell as owner, but he's not doing that out of the kindness or his own heart, he's an employee aswell as owner and will be paid a decent wage to run the club. If this new owner along with the other 2 decide for whatever reason they're not happy with the direction the club is going and want to change, there's really not much parish can do about it.
Let's look at it from uefas point of view, yes it's open to interpretation and there's loopholes in place but the rules state, no multi club ownership. So we qualify, uefa say, great news, crystal palace have qualified but there's a slight issue, textor is a majority owner at lyon and owns 40% of palace with a 25% share of vote, we need to look into this. Hello parish, what's exactly going on, oh dont worry about him, his only got 25%, we just ignore him. They're not gonna say that's fine, obviously they're going to open their own investigation.