In the facts given, where you are joint owner of a Lucknow property with your deceased father who died intestate, and the other heirs are your mother and brother, the following points address the sufficiency of documents for a clean sale:
A Legal Heir Certificate issued by the DM or Tehsildar serves as official proof of your legal status as heirs. Mutation of the property in the names of all legal heirs is a revenue record updating ownership that provides practical and official recognition.
For sale, either all heirs signing the sale deed together or the other heirs giving you a registered relinquishment deed (voluntarily renouncing their rights in writing) is generally sufficient to transfer ownership rights of the property. These documents, along with mutation, are typically accepted by buyers and banks as valid proof for sale and loan processing, especially when the property is undisputed.
A civil court order is generally not required in such a straightforward case of undisputed inheritance and mutual consent sale among heirs. Court intervention becomes necessary mainly when there is a dispute among heirs, minors involved, or refusal to agree on sale or transfer.
Therefore, for your case, a combination of legal heir certificate, mutation in all heirs' names, and a registered sale deed signed by all heirs or supported by registered relinquishment deeds from co-heirs, constitutes adequate legal documentation for a clean and marketable sale acceptable to buyers and lending institutions.
It is advisable to ensure that relinquishment deeds and sale deed are duly registered and all mutation formalities are completed to avoid any future disputes or challenges.
If you require more complex partition or face any dispute, you may consider seeking civil court orders, but for an uncontested sale with full consent, these steps suffice.