Sell GK1 - he'll be 22 next season, which means he'll no longer be a fast trainer and he doesn't stand a chance of reaching the quality of either of the other 2 by the end of the season.
On season 4, sell GK2 and buy a better one to be your first choice, GK3 will be better than him by that time, but will be a 3* player and more suitable as a reserve.