For example, research found that having strong relationships with siblings, improved the ability to negotiate with peers.
Hope this helped in some way :-)
If this is for coursework and you want to go into it more you can look into Richard Bowlby (Bowlby's son) who said that while a child has his primary attachment, secondary attachments are also required for them to achieve secure attachment. A secondary attachment figure is typically the person after the primary attachment figure who the infant has consistent access to. For example, for my nephew this person would be me because I'm essentially his "nanny" sort of thing who has him from 9-6 every weekday. This is what I referenced for this in the same coursework I mentioned above.