My point about the wheeling is this
In this condition the cav blue can't wheel to avoid the parent unit when they charge because that isn't the shortest line. Therefore they will end up like this
Yes they can.
Criteria one : charging unit must endeavor to bring as many models as possible into base to base contact with the charged unit.
This has not happened in your second picture, which means it's an illegal charge as long as the cavalry can wheel to avoid that situation.
Which in your picture they can. Therefore, they MUST wheel to avoid contacting the parent unit.
If they cannot wheel to avoid contacting the parent unit, (which could happen if they were much closer to the parent or if they were significantly wider, etc) they must declare a charge against both the parent and the detachment. They cannot declare against just the detachment and then choose to just clip into the parent unit.
You seem to be changing the meaning of the phrase 'shortest route possible' to mean 'shortest route that isn't possible'.
If a legitimate path exists to reach the charge target and only the charge target and with maximum base to base contact, the chargers MUST take it. If multiple such paths exist, they must take the shortest one.
They must take this shortest possible path to maximize base to base with the charge target , even if, for example, there is dangerous terrain in the way they'd rather avoid and they could avoid if they didn't have to maximize base to base contact.
The rules specifically say a charger is allowed a wheel during the charge to maximize base to base with the charge target. In fact, I believe it's a requirement.
And of course, we shouldn't forget criteria #4, which says that if possible, the charger must move to ensure that it is aligned to the target, if possible. (which it is, in your picture)
Note that you can basically do what you are trying to do (force the detachment and parent to be charged simultaneously) very easily by just putting the detachment and parent on the exact same line. If both are directly in front of the cavalry, and the cavalry is wider than the detachment, and the parent is on the same line as the detachment, the cavalry cannot execute unnecessary wheels if going straight ahead will lead to them maximizing against the detachment. In which case they would need to declare a charge against both the parent and the detachment.
so what you are trying to do still works, just the enemy wouldn't be disordered. There are other examples where the enemy would be disordered, if, for example, they were too close or too wide to wheel to avoid the parent.