Can admin access to web developer mean they can delete other administrators

Yes, if you assign to such user the ‘administrator’ role.
No, if you create a copy of administrator role and assign that role to a new user.
While User Role Editor active:
1) Only users with ‘administrator’ role can see/edit other users with ‘administrator’ role.
2) Users without ‘administrator’ role do not see User Role Editor in the list of active plugins and can not deactivate it.

Be aware if you allow to a user to install new plugins he can get a full access to the site in a minute – installing special PHP code as a new plugin. So you should trust enough to such user.