Dispute between property shareholders

We have an ancestral property in Andheri Marol - the property belongs to 5 family members, with shares agreed and divided by 3 parties A, B & C as follows: A - 2 members : mother + 1 son = 5.5 of 12 shares B - 2 members : 2nd son + wife = 5.5. of 12 C - 1 member : sister = 1/12 share the property needed maintenance as the roof and interiors were collapsing A approached B to have the maintenance work done. A got his brother in law (contractor) to do the work A said the cost will be around 5 lacs - may go to 6 lacs B agreed The work was to take place from March to May A told us he paid contractor 2.5 lacs, and B now needs to pay 2.5 B contacted contractor to pay the 2.5 - at which time contractor says it is not 2.5 lacs, the amount will be nearly 30 lacs B shocked said my brother told me it is only 5 may be 6 lacs contractor said, A changed the plans, wants to rebuild the whole house B got A on conference while speaking with contractor A got diffensive and said, he want to build the house B told A - "you should consult me your actual intent", the plan should have been amicably designed, with pricing, etc. all discussed and agreed upon. A - say I am sorry Question - A had cheated with former shareholders, and now for the past 10 years, they are giving B a run around - when they want to build B spent huge time and money getting plans from architects, etc. and A tells no I cannot afford to build, we must sell; then B spends huge money in ads to find buyers. We didn't get right price, so A says we must build as A cannot get a big space in that amount. COVID hit, then we left the matter pending. B - we need to know how to proceed in the matter. Please advise?