Limit total registration count across several products

What is the best way to set a total capacity for the combination of multiple products listed on a node? For example:

I have a bus that is limited to the total seats available. Lets say 50 total seats. Yet I have a different price for adult and child. In commerce I would set up two products:

Product_1 = myEvent (Adult)
Product_2 = myEvent (Child)

For registrations, the two products would need to be combined, as the total number of registrations for the combination of both products is limited to 50. All of the registration settings is the same for each product except for the capacity. The split between these two (number of children, or number of adults) is irrelevant. In this setup, one has to monitor the total number of registrations for each product and adjust as needed so that the total number available still adds to the total capacity.

Is there a better way, such as creating a base product with the registration and then separate products for the different rates?

Or is there a way to modify the module to span all the products attached to a node?

Interested in what others may have implemented as a solution, and/or where in this module I should look to add code if possible to add the feature.