My cousins (in their late 20s) fell out to the point that they now don't have contact. The male cousin (let's call him John) was not invited to (let's call her) Susan's wedding. Susan's new husband Paul has forbidden contact. Paul and John do not get on.
John had some mental health and addiction problems in the past which were very difficult and affected family life. John is now in full recovery and working hard on self improvement and doing things right. Susan refuses to talk to him now or in future.
John has a 5 year old son (Cal) who doesnt live with him but he has him weekends, when the child generally stays at John and Susan's mums house (my aunt - sorry if this is confusing!)
John is unwilling to let Susan have access to Cal unless they make amends between them.
Susan regularly sees Cal behind John's back -facilitated by my aunt who asks the rest of us in the family to not tell John - so as to protect him.
YABU - Susan has a right to haves relationship with her nephew and John should be letting her have access. It's ok that auntie facilitates Susan to see Cal being John's back.
YANBU - Cal is John's child and if Susan is unwilling to see John, John has the right to prevent her seeing Cal. Auntie is wrong to facilitate Susan seeing Cal and should not be asking other family members to keep this secret from John, to protect him or otherwise.