I read your consultation.
Even if it is called a tomb scavenger, it is actually a reburial (removal of bones), and it is necessary to store the bones somewhere. I think it is possible to first determine whether reburial is necessary in terms of physical aspects by checking the current maintenance costs etc. of graves, etc.
It probably depends on faith when it comes to praying, but there are many aspects that cannot be judged here. This is because he is your father, and the most important thing is whether or not you want to pray. I don't feel like praying at all, but since the soul dwells in our bones, isn't it necessary to repose for a soul? If you're worried, it's a belief you've learned somewhere, so I think it's better to pray as long as you have that feeling. This is to avoid feeling because of your father (= reward for not visiting graves) when something bad happens to you (even though that's not actually the case).
Visiting graves is a conversation with someone who has died. It's actually a conversation with myself, but I can have a deep conversation with myself that wouldn't have been born without the presence of the deceased. The fact that you are here now is also thanks to your relationship with your father, so even if that's not the case now, there will probably come a moment when you want to put your hands together.
There are no dead people in graves. Nor does soul dwell in your bones. Nevertheless, for people who want to put their hands together, I think the symbolic location of the deceased is the tomb where the bones were buried.
Living humans live by being caught up in visible forms. The deceased probably left their homes already, but since we are living people who don't know where to put our hands together then, I think we still need a symbolic place.