Complex sentence: While there, Anna becomes suspicious when the phone in her room is blocked and as she snoops around notices the experiments they are performing, and when Rowan learns that he has not heard from Anna, he sneaks into the facility to see his sister.
Split into simpler sentences: While there, Anna becomes suspicious when the phone in her room is blocked. When Rowan has not heard from Anna, he sneaks into the facility to see his sister.