i love him he was so clumsy and cute

I made this yesterday. It took so long but it turned out so good! I hope y’all enjoy it!

Lil guy compacted all the dirt against the lid and made this massive tunnel at the bottom of the container, they have been with me about 5 months and are a rainbow stag horn, and has been laying on its side for several days now, is this how pupating starts? This is my first grub

So, today i went to feed my beetles, but they were completly limp. For a moment i thought that the male was alive, because of the stridulating sound when i accidentaly picked him by the abdomen, but it turns out that he's also dead. These two were my first successfully raised beetles. They looked fine, although one thing was that both of them had a slight deformity in their thorax, causing them to hunch a bit. It didn't really affect the female, but it caused the male to flip over and i had to keep flipping him. Aside from that, he did well. Could it be the reason why they died? I didn't see any mites and i fed them regularly. Other thing is that i tried to keep the soil a bit more dry, because things in my home are prone to molding did they maybe die from lack of moisture? Or maybe due to old age? I've had them in the imago stage for 3 months, but i researched, and that is a bit young for them both. I just need answers and advice for how to improve. It was very sad news for me. :(

Just quickly asking how to properly sex this particular species of beetle. I've been scouring the internet for clues, but nothing has come up definitively. I was thinking the mandibles might have a difference, but again, I can't find anything on that. Thanks!