I don't know why people persist in hating Yoko. She happens to be a very talented artist whose singing voice is not what westerners (including me) are not used to hearing. I don't know if she's a nice person or not, never having met her or read much about her other than trashing. I'm tired of people blaming her and/or Linda for breaking up The Beatles. The reason the band broke up was simple: It was time to do so. The "lads" had grown up and gone in their own directions.
As to why Y & P don't get along, I think it's as simple as P has recently said: They're just different people with different interests. He has said he doesn't hate her, that he's indifferent to her and I believe him.
As to the credit thing, neither P nor Y has the legal right to change the credit. I think he knows that; I find it difficult to believe he doesn't with the Eastmans (some of the best entertainment lawyers in the business) as in-laws.