I have two macbook pro to trade in for a new one. Can I use two computers to trade in for a new one?

You will (may) get a gift card for each.

You may wish to consider selling them independently as this will likely get you more money.

Apple GiveBack [formerly: Apple Recycling Program; formerly: Apple Trade-up program] - All computer and mobile devices, including non-Aple brands - "Trade in your eligible device for an Apple Store Gift Card. If it’s not eligible for credit, we’ll recycle it for free. No matter the model or condition…" https://www.apple.com/shop/trade-in

The blue text in Limnos answer above is a link to the program. All the details are available at the link. click on the "Computer" tab part way down the page, specify Apple computer, and enter your Apple serial number (a self-decoding number) to tell them the model and standard features. They will discuss condition and provide a quote and shipping information. There is no obligation to complete the deal.

You can get an estimate based on year and condition, and send in your computer. If they agree it is in the stated condition, they will honor the price quoted, or if any problems, they will send it back to you free.

Also realize "we" are not Apple, we are other users like you. That's why we provide links (colored letters) to Apple's details of programs.