Can will be challenged in court?

Even registered WILL can contetsed.

If your grandfather did not leave any WILL then his property/whole estate shall devolve upon his wife, children equally. So your fther has share in it and can claim, until or unless hr relinquished by a valid deed.

Your grandmother hes bequesthed his share to you and you can submit the death certificate, WILL to the authority under whose jurisdiction property falls. If WILL is contetsed it shall be probated by court.

Engage an able counsel well versed with local laws and family/property/reveneue/civil matters.

THANK YOU VERY MUCH SIR FOR THE REPLY BUT I HAVE SOME QUERIES-
1 MY DADAJI DIED WITHOUT WILL,(NOR HE EXCLUDED MY DAD)
2- PATARI NAMED ALL PROPERTY TO TAUJI,
3- MY DADIJI AND DAD DIDINT BOTHERED TO BE NAMED AND ALL,BUT THEY HAD THEIR DUE 1/3 SHARE EACH IN IT
4 IF MY DADI TOOK MONEY FROM TAUJI,SHE HAD EVERY RIGHT TO TAKE ONE BOTH MORALLY AND LOGICALLY(AS SHE DIDNT CLAIM HER 1/3 WHICH WAS HERS THROUGHOUT HER LIFE)
THEN ON WHAT POINT IT CAN BE CONTESTED?

does probate of a will mandatory even if it is registered?

It is believed the deceased owners were HIndu.

Visit reveneu officer ( say Patwaari) or obtain thru RTI on the strenth of which document only one name of your uncle was entered in mutation record? 

As already posted: wife, children are ClassI legal heirs.

Did your grandmother collected money by siging some valid reciept/deed?

Children are liable to maintain the parents.

WILL can be contetsed on facts/suspicions sorounding the WILL.

If the WILL is registered itmay not be easily set aside on the counts of autrnticity.

Are the witnesses alive?

Leave all the points to a very able counsel.

Don't give anything in writing to anyone.

In presidential cities e.g. Madras, Calcutta, Bombay it is mandatory.

MY GRANDMOTHER MADE MY TAUJI PAY VIA CHEQUE...(NO MUTUAL PAPERWORK BETWEEN TAUJI AND DADIJI)-YES ALL HINDU FAMILY-

YES WITNESS ALIVE

Payment by cheque may not neccessarily amount to sale/relinquishment/gift/transfer/release/mortgage etc.

SO PAYMENT BY CHECQ IS A NORMAL(PLUS POINT TO ME) IS A NORMAL THING?

SO I ASSUME IT DOESNT SUPPORTS OTHER PARTY?

Engage an able counsel well versed with local laws and family/property/reveneue/civil matters.

KUMAR SIR I WILL, BUT IT SEEMS U R TOO AN EXPERT ENOUGH TO COMMENT ON IT ATLEAST.....

Frequent posts and PM's shall reduce the discussion to chatting.

NO final  advise can be rendered on gossip, hearsay, rumor!

Are you sure that GRANDMOTHER MADE MY TAUJI PAY VIA CHEQUE...(NO MUTUAL PAPERWORK BETWEEN TAUJI AND DADIJI)?

While the matter is being contetsed the OP's and their counsel will present their side/witnesses/evidences etc that you and your counsel shall have to counter.

Finally court shall decide.

If you can bring all parties to table and reduce the matter to amicable registered family agreement then it is the best. Thereafter it can not be contested.

Otherwise the matter may linger on till Apex court.

So weigh all pros and cons.

YES I AM 100% SURE THAT- GRANDMOTHER MADE MY TAUJI PAY VIA CHEQUE...(NO MUTUAL PAPERWORK BETWEEN TAUJI AND DADIJI)

YES I AM 100% SURE THAT- GRANDMOTHER MADE MY TAUJI PAY VIA CHEQUE...(NO MUTUAL PAPERWORK BETWEEN TAUJI AND DADIJI)

So far based on your posts  I have already posted what I could.

Beyond this; FInally; Engage an able counsel well versed with local laws and family/property/reveneue/civil matters...............................and let your counsel advise you and staisfy you on the basis of what you show and what you don't have!