Daniel, beautiful comment, thank you. I've already had similar dreams to the one you described, with my dad giving me his signature look while I made one of my classic sarcastic/flippant comments.
I also had a wild experience where I was painting the ceiling of a room and the paint drops on my mat made a perfect musical note. My dad played the guitar religiously, and I continue to get the feeling he's communicating with me through music.
I was raised Catholic, but haven't practiced religion in almost two decades. These types of experiences though make me seriously question whether I need to reevaluate my spiritual thinking, whatever it may be. Some may dismiss them as mere coincidences and attribute them to my desire to have my dad back, or you to have your mother-in-law back, but I truly believe these people are still with us as you suggested in some shape or form.
Thanks again for reading and commenting.