Hello! The "fan-like" lines are used to signal that two/multiple children are twins/triplets etc. I was quite confident you could turn them off as I know I've had them in my family trees, they annoyed me and I disabled them. However, I can't for the love of god find this feature.
In your tree, depending on whose family tree you create and for who, you could maybe try making one sibling born at "known date" and the other at "approximate date"? If you somehow find the option to disable this feature, I'd be curious
