Right now creating parents for individuals is alright, but I've noticed that there is no easy way to keep track of siblings, especially as you add more siblings to the tree. It would be great to have something like what we have for the parents when making the relationships for siblings that can just list them out then automatically links all of them together rather than having to go to each individual page and link every single sibling to all the other ones.
I think it would be great to have some form of input box for siblings (and possibly spouses too) that can have information put in like we have for the parents then have all that information be synced between the linked articles (Ex. I'm making John and he is related to Jack and Jill, by linking John to Jack and Jill in John's article, the article understands that Jack and Jill are also siblings and have the same parents as John), so you can organize a whole generation of siblings and (generally unless you are dealing with half-siblings) parents just using a single article rather than having to set it up for each article individually and run the risk of accidentally connecting Jill to Jack.
As said before it could also be useful for spouses, however I think it would serve a better use for bigger farming families and such, as generally people don't have 10+ spouses who are all married to each other too. Any use for spouses would probably just be a matter of UI cosmetics and ease of use more than anything in my opinion.
Yes, I wanted to show an uncle-nephew relation on a family tree recently but it really only caters to parent-child tracking. I couldn't show the uncle as the brother of the parent.
I like the idea in principle, but in practise this would probably end up limiting the number of siblings in the same way number of parents is currently limited, which would be less than ideal.
I have been wanting to do this with siblings and spouses, to better add more detail to them in the family tree.