Stick to Spain only. You don’t have enough time to visit Spain, a huge country, and Portugal. And April is the perfect time of year to visit Andalusia, which is very, very hot during the summer months. Check to see when the Holy Week celebrations are in Seville. This would be a fun time to visit but it’s also more expensive and very crowded.
In Andalusia you can visit Granada, Seville and Cordoba. These are small cities, (Seville is the largest) that all have important historical and cultural sites: Granada has the Alhambra; Cordoba has the Mezquita and Seville has the Alcazar. Each city is very different from each other, with different architecture, ambiance, etc.
You might also have time for Madrid. Depends on the exact number of nights you have in Spain. I plan by nights, not days.
So, a possible itinerary could be (after you visit your daughter in Barcelona):
Granada - 2 nights
Seville - 4 nights
Cordoba - 2 nights
Madrid - 3 or 4 nights
Fly multi-city, also called open-jaw. Into Barcelona and home from Madrid.