If you have space in your main panel for only a single breaker for charging, it is acceptable to install a sub panel fed from that breaker with a separate breaker for each branch circuit. That accomplishes the goal of sharing power from the first breaker.? The whole purpose of power sharing is for the TUWC to communicate with each other to not draw more amps that you set. That is the whole point. If you have multiple circuits you dont need power sharing at all. You just individually define the max charging amps per WC. Power sharing with multiple WC will allow a single WC to charge a full 48 amps if its the only one in use. If another car plugs in to another WC they will throttle down to share 48 amps or whatever you have configured in the power sharing for max amps.
There are also cases where you may have room for multiple breakers in the main panel, but need to limit your total power draw due to your service limit feeding the house. Installing multiple breakers in the main panel would be cheaper than installing a sub-panel and using the power sharing, you can keep the total power draw within your service limits. That is, assuming this meets code.