Colonel has it right: per the BRB, pg 100: "At the start of the combat (before Impact Hits are resolved), if a character's unit is in combat, but the character is not in base contact with the enemy, the controlling player can swap his position with another model that is in base contact. You can exchange him with rank-and-file model(s), including the command group, that are in base contact with the enemy."
It's worth mentioning that you can only make way with characters who are NOT already in base contact with an enemy, to replace non-characters who ARE in base contact with an enemy.
Is this correctly played?
Are impact hits resolved after make way, once in contact?
Can you switch positions during a charge move to avoid b2b contact of or with a certain model, or to be sure to have b2b contact with a model, before you are in contact with the other unit?
Assuming the two Tyrants were not in b2b contact after the charge, then yes he could make way with them to be in b2b contact prior to impact hits, then use the Tyrant's basic (ie. not modified by a weapon) strength plus the rank bonus of the unit (per the Ogre Charge special rule) for the impact hit of that model. This answers your first two questions.
Your third question is answered in the section: "Move Chargers" on pg 20 of the BRB. In summary, that section states that when you move chargers, you must move the unit forward with only 1 wheel of up to 90 degrees allowed. It does not allow reforming during a charge (which by definition is the movement of models within a unit - ie. repositioning characters). Note that this also applies to overrun and pursuit moves that contact a new enemy.
One last thing: BRB, pg 100: "Once the unit is no longer in close combat, such characters automatically return to the front rank of their unit at the start of their following Movement phase."
So after the combat, the command moves back into the front rank, then characters fill in - but not until the start of the unit's next movement phase.
-Snark