Purchase of Property from Co-owner after death of her husband

I am purchasing CIDCO property in Navi Mumbai. The property was in Joint name of husband and wife. After death of husband, the survivor (wife) has given indemnity to CIDCO declaring her legal heirs alongwith Consent letter of her legal heirs ( two son and one daughter) to transfer the property in her name and delete the name of her deceased husband from records. The indemnity letter and consent letter of legal heir is registered with registrar office. Based on same, CIDCO and society has transferred name in spouse name. The wife has now given irrevocable power of attorney to her son to do sale and transfer of property on her behalf. My questions are: 1. Can legal heir of the husband ( son and daughter) claim their stake in property afterwards despite submitting their consent form duly registered. 2. Though the Agreement to sale, revalidation agreement and possession certificate issued by CIDCO exists in original , allotment letter in original exists. What is process of obtaining duplicate allotment letter from CIDCO and can this be accepted by bank for loan disbursement. 3. I intend taking company (employer housing loan) loan and Bank loan for the balance. Can I create pari passu charge with Bank . CIDCO and Society NOC for Mortgage will be issued in whose name, my company or bank. Who will keep original set of papers. Can legal he