Complex sentence: Both siblings received painting education from their father and were part of his studio, with Barbara assisting in such projects as work on large altarpieces she also modeled, and gained some familiarity with the process of marketing her artwork to patrons.
Split into simpler sentences: Both siblings received painting education from their father and were part of his studio, with Barbara assisting in such projects as work on large altarpieces. She also modeled, and gained some familiarity with the process of marketing her artwork to patrons.