Is there anything to know about doing the towers? Are they available as part of a guided tour too? Is lighting better early or late in the day.
you can buy tickets directly from the Sagrada Familia website:
https://sagradafamilia.org/en/home
You can buy tickets just for the basilica or you can buy for the towers, too. The entire structure will knock your socks off. The towers, however, were not quite so impressive. If you've ever been to Notre Dame in Paris or Strasbourg Cathedral those were impressive.