Both Richie and Feech were a threat to Tony's position as Boss and both resented him for different reasons.
Feech, because he had a problem with a "kid" like Tony being his Boss,and Richie because he was an Aprile and should be the Heir to the throne.
They had the attitude that because of who they were at one time,and because they had done time for the Family, they should be able to "jump the line".
They both had to go, because it was only a matter of time before they attempted some kind of a move.

Ralphie,on the other hand ,while being a certified psycho,was also a ferocious earner. Even Carmine Sr. wouldn't OK a hit on him by Johnny Sac,because of the Esplanade cash fountain that he was in charge of.
Had he not been such a violent wacko,he probably would have had a long,profitable career with the Sopranos.

Vito was also an earner. There is a scene where Tony talks about him bringing in three times as much money in construction as any of his other guys.
His only liability was his sexuality. I think that Chase tried to portray Tony as a new breed of "Yuppie mobster", who felt "to each his own",but at the same time understood that Vito's case was beyond appeal.