Hi
1) Since you have the NOC from society, the transfer is valid in eyes of law.
2) however as a matter of abundant caution and to prevent future disputes, we advise that with the same set of documents namely NOC from society, News paper public notice, Death certificates of both parents, please also get a partition deed done amongst the 3 sons at sub-registrar office by paying a minimal fee.
3) Also please get the names mutated in the names of 3 sons in government records(electricity, municipality etc)
Hope this information is useful