The Team plan is meant for organizations of 2 or more that want to collaborate within the ChatGPT platform. You can use this for both developer centric and customer-developer applications.
It would resolve your issue of links being inadvertently accessible by others. If a custom GPT is built within the team and shared to only members of the team, no one will have access to it outside of the team regardless of having acquired the direct link in some way. The same applies to shared chats.
Note that the ‘monthly’ price of Team is $30 per user. The advertised $25 rate is when you pay annually.