Is there a way to model custom relationships between persons? GEDCOM seems to have this "ASSO" tag (for association), but I can only seem to create a "shared" fact between spouses in FTM.

For example, I would like to be able to capture relationships such as is-godfather-of, is-godmother-of, and is-godchild-of. I wouldn't even mind creating 3 shared events, and adding "godfather (of)" to the godfather, "godmother (of)" to the godmother, and 2 "godchild (of)" to the godchild; IF I could specify the other person as part of the fact/event/whatever.

As another example, I would also like to be able to model fraternal twins. This is a similar issue (relationship) although the direction doesn't matter (they are fraternal twins of each other).

Is there any way to do either of these things?

Thanks,
Scott