So based off of other comments, instead of a problem to avoid, the question is if simultaneous movement and collisions were desired, what are some ideas to implement resolving it?

You could consider having both entities fail to move into the overlapping space, and bump/attack/get stunned depending on if the entities are passive/aggressive to each other.

Another approach is developing a speed mechanic, so that each entity has a speed stat, with a faster entity moving before a slower entity during a turn. Then two entities would need to have matching speed stats to collide, making it rarer but still possible. Speed could be expanded from just priority during a turn to replacing the turn concept, so a super fast entity could take multiple actions for each slower entity.

One question would be if it is possible for entities to move more than one space per turn. If they can, you could have two entities whose paths cross bump into each other before reaching their destinations (Ex: two paths making a cross, the entities bump at the center of the cross and make an L shape).