Extrapolating on this (also thoughts only with no evidence and plenty of baseless speculation)…
Could he have been involved in her parent/s’ death in order to access the inheritance. It’s a pretty big stretch to think that her mum was murdered, but if the ex was also poisoned last year, and the mother passed away in 2019, the timeline is close enough to make another death of someone close to her worth a second glance?
Poisoning him maybe makes sense if he knows what she did. Maybe he told his parents something, particularly after his hospitalization?
I read Erin is 48(ish) so natural causes for her mother’s passing is also likely. As others have asked though, where is the motive to harm these people if she already had wealth.