Answer:
The for we would use is "<em>son</em>" because there is more than one person described in this sentence.
Explanation:
Frida Kahlo y Pablo Picasso <u><em>son</em></u> artistas=
Frida Kahlo and Pablo Picasso<u><em> are</em></u> artists.
Man, you like making my brain work, huh? Ha, okay, hope this helps!
:D