Are you going to be able to coach these kids through high school, college and maybe even pro ball? The answer is nope - at some point you wil have to cut the strings and turn them over to another coach. You may be turning them over to a great coach or you may be turning them over to a terrible coach but either way you have no choice in the matter. These kids will need to learn to how to handle coaching from a different voice or perspective or philosophy. With this comes to potential for adversity in not so good coaching. Turn them loose and let them learn how to overcome that adversity.
You said in one of your posts that your job was to get them ready for HS ball and you have. Now turn them loose so they can perform in HS ball. Like Coach May said it's only about 3 months long so it's not going to hurt them too bad if they do end up with poor coaching. Plus it's not fair to anybody if they play on two teams. Who takes priority on games if there is a conflict? What happens if it becomes too physically demanding on a kid - which team loses out on the kid?
Also, let's say you are playing in a big weekend tournament and the kid playing on two teams takes a high inside fastball to the wrist and breaks a bone. How can that be fair to the HS team who now looses a good player and it had nothing to do with their team and vice versa. These kids are on teams with other players. Those other players are depending on that one kid to help them win. It's not fair to the kids on that team to lose a good player when it could have been avoided. Plus TPM is absolutely correct in a player should never pitch for two teams at once.