Sibling confrontations arising from their deep -rooted hostilities against one another can create familial dificulties that can last for years.
unrequited > not returned/one -sided as in unrequited love> not the correct choice of word
From their relentless hostility against ../from theirmutual hatred for one another/from their mutual and reciprocal hostilities against ..> All ok.
From the seeds of their mutual and deep-rooted hostility , confrontations between siblings can arise to cause familial difficuties that last for years