Yes, you should be giving all committers individual credentials. Each developer should have their own account, so that changes can be traced to a specific person. Over time you'll get an accurate view of who best knows parts of code. As a bonus, when one person leaves the group, you don't have to change the password (lets pretend you would actually do that for the moment).
There's two parts two configuring this; Authentication and Authorization. Authentication is the process of determining identity. You can use htpasswd to do this, but it's better to integrate your existing password systems if possible. mod-auth-external can likely do this for you.
The other part is authorization; determining who is allowed to access what. The easiest way is to use SVN Authz and path based authorization to define a group.
For example, your authz file may look like:
developers = alice, bob, carla, trudy
developers = rw
alice = rw
developers = r