traveling to Spain and Portugal using air miles and fees

hard for someone to inform you without knowing what city you live close by as a point to depart and return to and if the air miles are good to use on any airline and if your ability to go depends on the use of air miles

Crossing the border from Spain to Portugal, or vice versa, can be more challenging than expected. Since you'll probably be flying to Mallorca anyway, I'd try to set up something like the following:

Mainland Spain or Portugal
Mallorca
Portugal or mainland Spain

With that sort of layout, you avoid the challenge of crossing the Spanish/Portuguese border on the ground or paying for a third mid-trip flight.

However, I have not checked on the availability of direct flights (or decent connections) between Mallorca and Portugal. Skyscanner would be a good place to look for those flights on budget airlines.

I flew into Madrid and out of Barcelona on United miles in 2016 without any difficulty.

There's a lot to see in Spain besides Barcelona and the Ballearic Islands. Maybe save Portugal for a second visit.

If you have not already done so, consider an open jaw ticket to get to and from Europe. That is, into one city and out of another. When shopping for that ticket, check out a number of different cities in Portugal and Spain, since once you are in the region, low-cost airlines fly all over those countries. Rick's web site has a page listing budget airlines by country. In most cases, you need to go to each airline's web page to get their fares and schedules. I suggest starting with Vueling and Easyjet. In most cases, budget airlines will be much less expensive than trains, and for short trips, buses may be your best choice.