Selling undivided ancestral property

Hello Sir, We have an undivided ancestral property in the state of Maharashtra. The property card (7/12) of the said property is having 8 names in total. All of them agreed to sell the property at certain price and decided verbally to share the amount in equal percentage (12.5 % each). However, at the time of actual sale deed, one person out of 8 is insisting for more %. We tried to convince him but he says he will not sign the sale deed unless his % of share is increased to 20%. Can other 7 people sell their share/ percentage of property even if one person is not ready, without any legal implications? And if this is possible by law, do we have to mention it in the sale deed that we are selling only our share of the property? If this is not possible, what are legal alternate solutions we have? Even the buyer is still ready to accept the deal without one's signature and he is ready to keep share of the 8th person aside(12.5 % of the total price). Please guide me on the issue as i got different opinions from different advisers.