Handle capacity on bookable things

Problem/Motivation

Hi,
I need to manage a capacity on my BAT units which are "vehicles". I have 6 seats that may be reserved by different people.
So when a reservation is requested or updated, I should ask for the number of people and see if cumulated reservations remains under the full capacity.
I have looked for documentation that could explain how to handle this functionality but found none.
So looking for feedback from developers would have done similar things.
Thx

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes