I also had a close in-law who was on Bataan death march. We never knew the scope of his whole story until he died (he had dictated it to a survivors group and the VA which was released later). After Bataan, Corregidor, and the Hell Ships, he eventually wound up in Manchuria in a coal mine.
We kids would only get small snippets of the story. Like the time my brother brought a Taiwanese classmate to the house, and he started conversing with that person - in Chinese. Everyone was like “What the heck? he speaks Chinese??!”
He grew up dirt poor, and joined the Army in 1939 to get 3 hots and a cot. He survived because he was young and tough as nails
One of my Dads friend was a wwii vet that was a guest visitor of the Japanese empire. The guards brought them English language Japanese newspapers . He said they were amazingly uncensored . He kept up with the war reading those newspapers.
I think my uncle was doing the same thing, but he joined in 1933, and arrived in the Philippines in November of 1941. I sometimes wonder what was going through their minds, on Dec 7th, 1941? They might have known the Japanese were coming.