Welcome to the forum. You are going to find this an amazing place, because whatever you ask, whatever you experience, others have been there and done that already. It is a mine of information, plus the people are kind and compassionate and insightful.
It must be very very distressing for all three of you, your Dad who does the crying, your Mum who must feel so helpless, and you trying to be there for both of them. And you visit daily.
I was feeling so upset, looking around for some brilliant idea, and then I read Lin1's post..... that will give you fuel to experiment around with and somewhere there will be just the thing to bring your Dad some relief.
I certainly agree that people don't cry for no reason, and this is just as valid for people with dementia.
My Mum (who is still at home with us, so not comparable) has recently been put on an anti-anxiety pill, as she was getting so obsessed with this and than, there was always something that kept her fretting. I was worried about addiction (Mum is 85!!!) and anti meds like this. People on the forum helped me see through my blind spot, and now we are considering increasing her dose to two a day - BECAUSE BEING ON AN EVEN KEEL is quality of life.
I very much hope you will find the solution that suits your poor Dad very soon. Leave no stone unturned. Hope to hear how things go for all of you regarding upsetting situation.
All the very best, BE
