Hello @Anastasia
It is with much sadness to know of the present experience of you and your family. Though my Mum was in residential care during her last three years, I was with her each day, so can empathise with your feelings. During the last three days of Mum's life, all that I could do was sit and read while I was with her. Before that I read to her from a series of seven books by the same author.
All that I can offer as a suggestion is something similar. To sit and read, either "out loud", with your Dad, or silently, on your own. You are aware of the inevitable, so occupy yourself in a way that would be meaningful to both of you, as it would have been before. I did not find the reading prevented the feelings that I experienced, the sadness and the tears, but rather was a means of filling the additional time in a meaningful way.
With Love and Best Wishes
@HenryX