I don't believe in Freud's "wish-fulfillment" theory about dreams. (That would be that you secretly wish that he loved your family more than his remarried family.) But I'd need to know more about how the dream-scenes developed in your dream. How the lighting, locations, and family imagery changed as the dream changed from your family to his second family.
I remember from over 25 yrs ago that I visited a men's group of men in their 80s, in which those who had divorced and remarried mostly said that they wished they had just stayed with their first wives. From what I know about the inevitable disappointments in marriage (that are due to a certain blind belief during new love--3+years--that the wife- or-husband is perfect4us because s/he's JUSTLIKE ME--but in fact the brain/mind's habituation to first marriage makes second marriages NOT as comfortable as first ones. Because the second doesn't fit as well into one's brain-mind patterns than the first one did (since that's when those patterns were actually formed).
But I'm not assuming THAT's the real GreatWisdom of your dream. For this dream is a guidance tool for YOU, not ME.
So 1. What do YOU think are the main DIFFERENCES for HIM between his first marriage & family (that included YOU) and his second? And what were the Differences in the way that YOU looked at him?
2. This dream has come to teach YOU something NOW. What is going on in your life NOW that might benefit from this demonstration of your father's levels of happiness in your family and in his second family? (Could you be considering divorce?)