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While I could end up wrong, I'm going to have to disagree that all 3 of them being found dead is suspicious. Sure, if the dog hadn't been crated, and perhaps even if the other 2 dogs were found deceased inside the house as well, yeah, that's suspicious as heck.
But, he was 95 years old. Death of a 95 yo with a heart condition isn't at all surprising to me. Neither is the dead dog because it was locked up! It couldn't get out to fend for itself.

Due to the dog being crated I'm taking it out of the equation. Now we have 2 dead people, dying about the same time.
While it is a little odd that Betsy was also deceased, and at a young age of 63, we don't know if she had any health issues.
What I'm putting my money on is that Betsy had the first incident. She was likely going to take her daily meds and whatever happened, happened. An aneurysm? A heart attack? For her it could have been fatal or not.
Gene hears her fall to the floor due to the ruckus the heater and dropped pills made. She might have even made some sounds of distress. He goes to see what's going on, finds the scene as it was (her on the floor, overturned heater, and scattered pills) and hurries off the best a 95 yo that needs a cane to walk can hurry off to get help.
He's distressed. He's upset. He's scared. Just even the initial sight of his dearly beloved on the floor either deceased, or in distress, is going to upset him greatly. He got hit with a flood of adrenaline, his heart is pounding, he can even hear it in his ears, and his blood pressure shoots through that roof and down he goes, likely dead before he even hit the floor.
IMO that's what killed Gene. As for Betsy... her event either killed her right away, or shortly after. Or, she could have been very much alive like the poor crated dog, just unable to get back up and died where she laid for days with no help coming. Her death likely was the same as the dog's if she didn't die immediately. No food and no water for over a week.
It's all very sad, and is likely the only reason this thread is going gangbusters, is because it wasn't just a 95 yo movie star that died. His deceased wife and dog were found at the same time he was. While all 3 deaths are sad, it's my opinion that their causes are easily explainable and not suspicious.
I am also willing to eat crow if I'm wrong. It's just where I'm placing my bet at this time. All natural.