it seems to be it would be common sense that it is a good thing in relationships to have compatible descendants. is this true? what if two people have incompatible descendants like libra and taurus? would this be enough to create a clash the relationship?
Emily, this sort of makes sense, but it's probably more important to consider relationships between planetary pairs. In your example, both Taurus and Libra are ruled by Venus. We would want to look at the situation of Venus in the individual charts and in their synastry.
Then the opposite signs would be Scorpio rising and Aries rising. So we should look at Mars (traditional ruler of Scorpio) in both charts and in synastry, too, while we're at it.
No single factor in the synastry can make or break a relationship. It depends on the big picture.
It is considered ideal for couples to have ascendants that are either in the same element (both water, both air, etc.) or the same polarity (water and earth or air and fire). That would also make their descendants the same element or polarity.
But if they're not, that does not make the natives incompatible. If they are, that does not make the natives compatible, either. It takes the whole chart. Every pair of people has some "incompatible" placements in their synastry. Couples, best friends, and other close relationships form and endure in spite of that, all the time. There are also people who do not get along with each other despite having compatible AC/DC axes.
If their AC/DC axes are in different polarities, like in your example, look for how else their charts might match up. Both of these people have a DC ruled by Venus and an AC ruled by Mars. What are Mars and Venus doing in their individual charts? And in their synastry?