Calling Barcelona experts

Possible yes, advisable no. Are you on a cruise with only a day in Barcelona? I rate Sagrada Familia as a a three hour minimum experience and best to be there first thing in the morning with tickets pre-purchased. I prefer Casa Batllo with a minimum two hours. La Pedrera is just up the street from Casa Batllo.
However, how much architecture can you take before going on overload? Please define if this is your first trip to Barcelona and the total time you have to spend in terms of when you arrive and depart. This will assist folks with being able to help you. Safe travels

I'm planning to spend 4 full days. (maybe 5)

Then why cram all three into one day? I figure Sagrada Familia as roughly a half-day by itself. You might want to read up on Casa Mila (La Pedrera) and Casa Batlo and decide which to see, instead of doing both (the entry fees are pretty steep for roughly the same experience). In my opinion, Mila is prettier from the outside, but Batlo is more interesting on the inside.

Sagrada Familia is definitely a half day deal and you should buy tix in advance. I can't imagine seeing the other two in the same day (or wanting to). Agreed that the admission is steep for LP and CB. I'd pick one or the other. SF is worth every cent.

I envy you for planning 4 to 5 full days in Barcelona. My family spent 9 days in Barcelona and still had plenty left to do. I agree with the other posts about picking only one of the two buildings. BTW: after visiting Sagrada we purchased a picnic lunch and caught a cab to the Parc and spent an enjoyable afternoon.