5%of the basis of all property includable in the gross estatefor federal estate tax purpose, please translate to layman terms?

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Perhaps, this question should be in the probate category? Two of my siblings were given administratorship through the court in order to handle the sale of property, now we are at the brink of selling and we have to sign papers for the lawyer to proceed with the purchase and sale agreement.. None of us are very knowledgeable as to how this whole procedure plays itself out. The clause referenced to in my question was in the lawyers retainer agreement. We understood that in New York city a closing is usually around $2000+/-. So, this 5% has gotten our attention. If someone can please answer in plain terms it would help us greatly. Thank you.