1)check sanctioned plans by muncipal corporation
2) file RTI application and obtain sanctioned plans . consult a local architect
3) if builder is carrying on construction on the plot purchased from 4 owners contrary to sanctioned plans and not keeping marginable distance as per development control regulations then move court and seek injunction restraining builder from carrying on further construction .
4) merely because caveat is filed by builder does not mean no stay would be granted . only that court will grant stay only after hearing both parties .
5) plot purchased by your father by regd sale deed belongs exclusively to your father and it cannot form part of common access