Margareth: What I tried to tell you: If you had started by merging the two Isac's, at least connecting them, you could click in the triangle on the Rose node in the tree and successfully go through the selection of the correct parents without getting the cannot split the tree error since he also would be connected as her brother.
Also: Since the wrong parent set: Isac and his wife was duplicates of her brother and wife without any further connections you could just have merged the Isac father and wife into the her real parents Hartvig and Esther. No profiles would be lost and no bad connections would follow that merge since they were unconnected (and also explaining why you got the cannot split the tree error).
You just had to look another way when merging two profiles which did not match and hurry to resolve the data conflict before anyone complained. The result would be correct anyhow and your problem solved.