When a woman shows up claiming to be the rightful heir to Woodstone Mansion, Sam and Jay enlist the help of a lawyer. And a surprise event takes place that could dramatically change life at the manor.
I think Trevor did know or did suspect but didn't ask because he wanted her to say it in her own time.
Remember in TP, when Sam said she was curious but she didn't know the etiquette around ghosts' deaths. Trevor doesn't really look like he wants to talk about it. And in fact, he never talks about his death.
I've made this point before, but Trevor is the only younger ghosts that never brings up his death in any capacity. The ONLY time he ever talks about it is in TP or when someone brings up his body in the lake and usually he brushes it off.
That is a level of avoidance most of the other ghosts don't have, except Hetty and Sass. They're the only two that have avoided mentioning their deaths.
So, it would make sense for him to see the evidence but not ask and then to lie to the others about it becuase he understands that each ghost deals with their death differently and Hetty, like him and like Sass, might not want to talk about it.
I knew Brandon Scott Jones (Isaac's actor) could do drama even in his usual flamboyant image because of "The other two", but I've never seen Rebecca Wisocky in anything else, and... wow.
Look, I've seen a lot of heavy drama reveals on TV. But her pulling the cord out was fucking heartbreaking, and she didn't even say anything, just... her face... Oh my fucking god.
Hetty: BE A BETTER PERSON!
Trevor: WHY?!
Hetty: BECAUSE SOMEONE NEEDS TO HAVE MORALS IN THIS RELATIONSHIP, AND IT SURE AS FUCK AIN'T GONNA BE ME, SWEETHEART!