Not true on both counts.
Killie offered McKay a contract, something showed up in his medical and they withdrew the offer
Given was on a YTS contract that celtic had not converted into a pro one. Blackburn stepped in signed him on freedom of contract. Anyone that watched youth games at the time will know he kept the score down in a couple of games against Rangers.
Sinclair released a lot of players that are now playing at a decent standard, and replaced them them with bigger, stronger players that are now in the main playing junior and pub football.
To be fair in Harry Cochrane's case I believe he asked to be released due to lack of game time. At the time Rangers had four players contesting two centre mid roles, one being Billy Gilmour. In saying that the HOY's job is to identify and nurture any talent, which Hearts obviously did. Falkirk also identified and developed four players he released and made close to £2 million in transfer fees.
I think Harry's father is a scout for Rangers.