Terminal services needed with client access licenses?

Please excuse the probably dumb question but I haven’t been able to find a clear (to me anyway) answer 🙂

I have a small business client running real estate software on Server 2003 Standard. They now have real estate software running on the server and find they need access by up to 5 people at the same time.

I’m very familiar with computer support (20 plus years) but not server software.

My question is can I just install the licenses on the server or will I have to setup Terminal Services, Active Directory, Domains, that kind of thing?

I need to keep this as simple as possible while I learn and also have an issue with busy real estate agents with minimal computer knowledge.

Thanks in advance for any help you can offer.