No, it is not necessary to get demolition approval before going for partition. As such there is no rule. It is a matter of convenience that a land can be conveniently partitioned comparing a built up house. If your father, his brother and sister mutually agree then they can carry partition on mutual terms in respect of all land including built up house also. 

If the currently dwelling house property is habitable and would be an unjustified act if demolition process is proposed then, it is not advisable to go for demolition. Since it would be an amicable partition on mutually agreed terms, the partition can be decided by both and to compensate in terms of money if the other one is getting a better share in the property.

The property can thus be partitioned without causing any damage to the existing good structure.

It’s not mandatory depends on your discretion 

As rightly advised by your counsel, if you do not obtain a demolition approval, you may get only an undivided share each. If you do so, the underlying land parcel can easily be divided by proper metes and bounds and each of you can get your specific portion duly marked and divided.

No need of approval.

And in your case, if partition is not equal than settlement deed will execute.

- If the said building is floor wise ,and your father , brother and sister is residing on separate floors of flat of the building , then each technically each having to things.

1. First is the constructed part of the building where you are actually residing , and

2. The Second is a proportionate share of the land on which the property is built, and this share of land allotted to all the sharers and this is termed as undivided share in the land.

- Further, the value of the said flat/property is depend on the UDS, and constructed area i.e. Land rate will increase and not the value of the constructed flats rate. 

- Hence, if all the sharer want to stay in the respective portion of the building , then the demolition approval of the building is not needed or execution a partition deed. 

The requirement for obtaining a demolition approval before executing a partition deed depends on the local laws and regulations in your jurisdiction. In some cases, obtaining a demolition approval may be necessary if there is an existing building on the property that needs to be demolished for the partition to take place. 

If the lawyer has advised you to obtain a demolition approval, it is important to comply with this requirement to ensure that the partition deed is legally valid and enforceable. Failure to obtain the necessary approvals and permits may lead to complications or legal issues in the future.

Additionally, your lawyer may have recommended obtaining the demolition approval to ensure a smooth and hassle-free partition process. By securing the necessary approvals in advance, you can mitigate potential conflicts or objections from authorities or other stakeholders involved.

Yes it is mandatory to get demolition approval if the building is dilapidated conditions and hazardous to the neighboring buildings/structures etc.,