Could you please allow people to add a sibling without knowing who their parents are.
I have quite a lot of Irish family - for instance, in my family, 2 brothers came over together from Ireland, lodged in the same places here in England, both married in the same church within a year of each other and lived next door to each other with their respective families. Yet I can't add the brother because I haven't YET found the birth records in Ireland with their parents names!
I know they were brothers because my Great Grandmother told me the story of her Grandfather and his brother before she died when I was 15, the census' and records just backed up her story.
I don't want to make a whole new tree just for this one story!