That's funny because my father has Scorpio sun and Taurus moon, and my mother Leo sun Gemini moon, Aries and Cancer ascendants, and they've been lovingly married for over 40 years
That's very anecdotal, one in a whole dozen probably. If you want more information on where I'm getting my theories from. Your parents do have one connection though (Cancer asc and scorpio sun, cancer asc and taurus moon, and I'll bet that your dad's moon is in krithika which is the yoni of cancer asc pushya like my parents which I will go deeper into)
1. Carl Jung who did research on couples who had sun-moon connections
2. Basic theory about the zodiac and I'll link a video to it, of a man who'll explain it in a more articulate way.
Another thing that I didn't talk about, is nakshatras that also play a role in compatibility. So it's quite likely that your parents had nakshatras in which are compatible in nature.
Another thing that is also likely, is that they may have good ability to form relationships in the chart itself. Again as I said and I'll say it again, research holistically should be taken more into account as well as what older astrologers had said. That's all I'm trying to get at.
https://www.youtube.com/watch?v=qvPZM7Fwqr8&list=PLqnDwobT_2hDJ5aQafXFUely7gYQib4Ru&index=3
This is a video I highly reccomend.
https://www.youtube.com/watch?v=16x3oGdfpDQ&t=1357s
https://www.youtube.com/watch?v=Ab1NxwcIuC8
Another two videos I highly reccomend. And although they are long, they are vital in understanding the nature, historical background and logic behind astrology and how complex it is.
This is what I do, I extract my information from a theoretical framework set by an old, taught astrologer (parashara, jaimani, or ptolemy), and I'll try and see it through the lens of a modern astrologer that has done their techniques in a way that works. I'll put even more emphasis and weight on researched aspects. And I use a site called capricorn research.
For example, Carl Jung's research verified the theoretical framework already set by astrologers from before that sun moon connections with similar signs is important. Now that doesn't mean it's the be all, or end all, because there's other factors such as nakshatras, whether someone is capable of forming a relationship, and sometimes in the case of nodes/pluto/8th house, I've found if the link is strong enough with out the compatibility, couples still remain together although they bicker.
My parents as well has sun-sun connection, but their moons were in different elements(BUT THEY WERE IN COMPATIBLE NAKSHATRAS). So my mom's moon was in gemini in the nakshattra of krithika and my dad's moon was in cancer in the nakshatra pushya, and they are the yonis of eachother.
So the thing is honestly, there's a theoretical framework in place, with some limited research to use, but there's two things missing I find. 1. integration of multiple techniques 2. How much weight should you put in each theory 3. Most people haven't even decided on a house system, or the type of zodiac.
I hope I make sense. And I've heard before many times, 6th house, 12th house, and 7th house are enemies although people say 8th house are people we are attracted to but trigger us at the same time.
Secondly, I have another theory and I don't know how true this is. But let's say you have a sun in leo conjunct neptune, and a sun in pisces. Although they are two different sexes and elements, because the sun in leo is conjunct neptune, they might as well get along because of that. I'm not sure how valid that would be, and have no way to test it out as there are a hundred third variable issues. If another astrologer wants to comment on this, please feel free to.