Hi Halo
I have learnt from TP that When it gets to this stage you really need outside help.
Can you or your dad arrange a GP appointment to explain what is going on and that your dad is "at risk"? There may be some medication changes that could help calm your mother down.
One thing that you can do now is to ensure your dad has a safe room to go to with a lock on the door and a phone, either in the room or on his person at all times so that he can get help. People with dementia can be unexpectedly strong when they are aggressive so he must be able to get out of harms way.
I know my MIL's aggression eventually passed, but not for quite a while. I expect more experienced TP'ers will have some more constructive advice for you