A registered WILL is unlikely to be set aside on the count of authenticity.
Once probated it shall bear the stamp of court.
A registered WILL can also be contested.
The authority under whose jurisdiction the property falls can transfer the property in the name of beneficiary in the WILL as per set rules. The rules may include condition(s) that all other legal heirs (other than beneficiary) may sign NOC and/or WILL may be probated OR no such requirement may be imposed as per the rules. You need to examine the rules.
The occupant may inform the society that WILL is challanged and suit is pending to be decided by court.
The society may demand the pending dues from occupant or all legal heirs as per its rules.
You need to examine the rules.
Rest your lawyer that has examined all docs on record can advise you better, including on time, merits, actions etc.