So... Your issue isn't going to be getting them what they need. Your issue is gonna be need High Availability and scalability. To give them info, you can create a VPN, or some sort of tunneling service. You can migrate to a cloud service such as azure, AWS, or Google cloud.

Scalability means that if your business expands, it'll be easy for you to expand computing resources, without the need for redesign (this gets expensive). Also you don't want to be stuck paying for services you don't use. No sense buying a $1k server, if a $200 server does the job. But that $200 server might not be enough next week.

High Availability means, if the server your instance is on goes down, it will automatically populate on a different server, so your employees/interns never lose connectivity.

Once you decide that platform, you need someone who will administrate users and privileges, backups, basic IT support to those in the field.

This is typically what a MSP handles for businesses. Designing, the system, and the way the system is maintained is why ppl get paid the big bucks.

This is why, most businesses hire a IT professional to do this. They should know, saas, paas & iaas. Know which one is right for you, help you decide which cloud platform you go with, and which security measures you go with.

Now you'll likely find a solution that works on this subreddit, you'll likely find cheap solutions, overly expensive solutions, and secure and insecure solutions, and everything in between. I'd be looking to either hire a system administrator, or a MSP to set this up right from the getgo. If you feel you are up to that task, by all means. But, as someone who ran a business, and is now looking to get into this exact field. This is a full time job you are giving yourself.