Can I sell hotels I have contracted myself alongside the ones coming from the hotel API, in the same search?

Yes, in most setups you can sell hotels you have contracted yourself next to the hotels that come in from the API, and both can appear in the same search results. Agencies often have properties they have negotiated directly, and there is usually no reason those should sit outside the portal.

The usual way this works is that you load your own hotel into the system once, with its description, photos, room types, board options and the rates you want to sell at, along with the dates those rates apply to. When a customer searches that city, your property is checked against the same dates and guest numbers as everything else, and it appears in the list beside the supplier results. The customer does not see any difference, and the booking lands in your reports like any other booking.

There are limits worth knowing about. Whether this is included depends on your plan and on how your portal has been set up, so it is worth asking rather than assuming. Availability for your own hotels stays your job, because that hotel is not sending live updates the way a connected supplier does, so if rooms sell somewhere else you have to reduce them yourself. You may also find the same property arriving from a supplier as well, which can show up twice unless the two are matched together.

Check with your account contact whether direct contracting is switched on for you, and if it is, start with a single property so you can see how the loading and the availability side really feel before you move the rest across.