Since a ground character can move through a friendly character a situation occured in our game. If a moving ground character moves through a friendly character's square such that it would place them adjacent to an opposing grounded character, is this illegal since movement would have to stop at that square and you can't occupy the same square with two pieces?

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say that a and x are friendly ground characters and k is an opposing ground character. Say that a has two squares to move and it wishes to land on j. Would it be illegal to go diagonally through it's friendly character since this is adjacent to an opposing grounded character and they would have to stop movement there which they can't? Thanks

You are correct. That would be illegal.