How can I reverse a bad merge?

Someone has merged a completely differently family with an ancestor in my well documented tree. Now my ancestor has two sets of parents and a while lot of unrelated siblings and I can't break the link. Is there some who can help me separate these people out of my family?

My ancestor; https://www.geni.com/people/Arthur-Williams/6000000072068866963

Bad merge is here https://www.geni.com/merge/view?revision_id=75356329920

Unrelated parents 



Unrelated siblings

George Addams Williams
Herbert Addams Williams
Roland Addams Williams
Godfrey Addams Williams
Harold Addams Williams
Mary Addams Williams
Unknown Addams Williams
Unknown Addams Williams
Unknown Addams Williams

Arthur's Real parents

Leonard Williams, Bishop of Waiapu; and  Sarah Williams 

Real siblings as documented in our family records: 
Frederick WilliamsEmily GrayEllie MacLeanEdith WilliamsHerbert WilliamsAgnes (Williams) GardinerAlfred WilliamsFrancis Williams and Sydney Williams  

Thanks for any assistance 



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