How to add existing person as partner or parent etc? Is there any way to change relations (make the lines) after person box creation?

Example of situation; I create a person, and then 2 parents for the that person. Then there is a sibling for the same person, but with different father (ex of the other partner). In current system I found no way to make all connections: I can add sibling to the 1st created person, but there is no way to indicate father to that sibling (from the existing ones). Also, it is not possible to determine one's ex or current partner status from existing ones (i.e in the example here, I create a Father to sibling 1st, then try to add him as ex to mother created earlier for 1st person)