Can I let other small travel agents sell through my portal with their own login and their own prices?

Yes, in most cases you can let other agents sell through your portal, although how many logins you get and how much you can change for each one depends on the plan you are on.

The usual way this works is that every agent you sign up gets their own login to the same portal. They search and book in the normal way, but they only ever see the price you decide to show them, not what you pay the supplier and not which supplier the fare came from. You set a separate markup for each agent, or for a group of agents, so someone who sends you a lot of business can be given a better rate than someone who only books now and then.

On the money side, you normally decide whether an agent books against a balance they have paid you in advance or against a limit you allow them, and the portal stops them booking once that is used up. Every booking they make shows in your own reports and statements, and you can switch a login off at any time. The thing to be clear about from the start is that you stay responsible to the supplier for whatever your agents book, so a cancellation charge or a wrongly typed name is still yours to sort out.

One honest limit is that some suppliers have rules about who their content may be resold to, and that is set in your contract with them rather than in the software. Before you promise anything to your agents, check your supplier contracts and ask which of your connected suppliers allow their content to be sold on this way.