My divorced brother died 10 months ago with a valid will in which he left his estranged son only $15. Why do we have to go back to court?

My divorced brother died in June 2020 with a valid will leaving his only child, who is estranged, only the sum of $15, and the rest to our Mother (widowed). After a (Zoom’d) January court hearing, as of April the letters testamentary were issued (and back-dated to February). We have a buyer lined up for my brother’s main asset, his house, and to keep things as simple as possible, want to get this done since my Mother is elderly. But Yesterday we were notified that there must be Another court hearing to okay the sale because the estranged son is “not being cooperative”. Can he hold up the sale of the house? He has not formally contested the will to our knowledge.