For example, with helicopters, only the purchaser can install a lock.
Would it be possible for team members to install a lock?

This is a reasonable suggestion. I will aim to add it over the course of the next week. The plugin already has some awareness of teams, so it should be easy to add via a new config option along the lines of "Allow deploying locks onto vehicles owned by teammates".

Added support for this in v1.14. Please try it and let me know if that works for you.