No. They did not necessarily know that van was in Gabby’s name only. Many parents try and at least partially succeed in staying out of their kids’ business especially when SO’s are involved.
Ive known of several situations where a couple or siblings , cousins, whatever, who share a vehicle, bank account, apt even a house and it’s just in one person’s name. Sometimes not in the name of the main contributor to the account , asset, lease, deed. Sometimes it worked out fine. Sometimes it did not.
My son was engaged for a couple of years before he married snd I was not privy to whose name was on what except by happenchance.
The Laundries probably had a lot to say to BL when he returned without Gabby, in terms of her belongings there. They may have asked what happened and where she was, but not pressed when a very upset BL said he didn’t want to discuss it right now. Given it a bit of time. They likely had no inkling of the horror that had occurred. It would not have entered my mind either and I’d have let it rest for a bit.
MOO, the tests, emails, etc from Gabby’s family were likely what let them know something was very wrong. And they chose to get professional help in dealing with it