Gilda,
I was hoping you would reply as it would be wonderful for Bessie to be able to share with you, the letter that your Dad sent to her mother.
I would also be able to fill in some of the gaps of your knowledge about your father, in particular the fact that he was never in Japan.
He also arrived in Singapore just 2 weeks prior to the surrender, so its difficult to imagine that the group photo would have been taken at that time.
A stronger possibility is that it may have been taken whilst he slaved in the sugar factory at Heito, but maybe the dress code of the photo may rule this out.
Hoping you will reply.
Mike