There is no other option practically available other than registration. If they want to sell it.....they will, today or tomorrow. 

Your father can execute will bequeathing undivided share in property to your mother and 3 sons 

2) your brothers would not be able to sell their share during father lifetime as will takes effect on death of testator 

Yes the property may not be sold as of now. If anybody wants to sell in the future he is to ask the other brothers first and they have the right to first purchase the property.

You may also purchase the whole property yourself.

But once you register the property in their names ie you and your brother's name you can't stop them from selling the property.

1. Once the different floors are given to different sons then each son becomes its exclusive owner and hence is free to transfer if in his own way.  No one can stop him legally. 

2. Since there are more than one co sharers it's worth demarcating the respective shares. Your father can nevertheless mention respective undivided share without physical partition but in that circumstances also one can mortgage his undivided share. 

3. A private trust with restriction on sale to a stranger is though an apposite option here. 

1. See in case any legal document/instrument that is settlement deed or gift deed is made then you all will be the absolute owner and may sale same you cannot stop them from mortgaging or selling their share in the property. Also, Power of attorney is not an instrument to transfer the same so using the same you cannot have rights on the property.

So in case, your father wants to transfer the property either he has to give complete rights or he may make a will giving rights after his demise. 

Dear Sir,

One of the better idea will be to get a WILL from father as per his desire because the property will remain with father during his life time and any division will be possible only after his departure to heavenly abode. By this method, the intentions of brothers will not succeed and the property will remain intact and all the members of family will have right. 

Hello,

1. You can allow the mortgage agreement and share the rent proceeds along with your brothers and ensure that in the Mortgage Agreement that your father enters into will have specific clause stating that the rent shall be paid to the brothers proportionately in their individual accounts.
2. In addition to the mortgage with the clause regarding share of rents, it would be advisable that your father execute documents either by a registered Gift Deed or a Will to allocate your respective shares so that in case of his demise there will not be a dispute.

You can execute Registered family settlement deed or partition deed in the said case

1. Father can execute a registered "Partition Deed", with mutual consent signatures of his Children, with strategic clauses clearly defining the share ratio & description of property & rent benefits  being given to each individual person.

2. AFTER above each partition portion can be individually mortgaged.

3. IF Mother wants that everybody should be together, THEN Father can create a registered "Family Trust" and transfer all his properties to the Trust and all rental income will go to the trust, AFTER which the rent can be distributed equally to each Trustee (family member only).

1. If the individual floors are registered on individual's names then they become the owner of their respective floor in the building with clear and marketable title on their names, meaning thereby that they can sell their property individually as per their will and wish. 

Sentimental feelings do not have place in the law, they are not legally bound by your wish or your mother's wish to stay together.

Therefore you may find a solution for this amicably instead of looking for legal ways to solve it.

2. In that case your unwilling and adamant brothers will again opt for mortgaging the entire building thereby you will run  a danger of losing your entitled property too.

You better get your floor registered on your name along with the rights for the common areas in the complex so that you need not be worried about what happens next, you can keep your mother with you in the same building  to fulfill her sentimental needs as well.

Your father have to execute settlement deed to transfer each floor with proportionate right in land or WILL which will be effective after demise of father.

WILL can be conditional with no right to sell the property than brothers cannot sell their respective floors.

Please get 3 Special Powers of Attorney FLOOR wise from your father and get it registered with Registrars of property under Indian Registration Act. 

According to SPA each one  of you would be authorized to carry out activities as per your wishes without disturbance and hurdles to each one of you.

Best possible solution to your query is ask you father to Bequeath the property by way of Will to all there of you with a condition "NOT TO ALIENATE" the property, so that, the entire property will in tact.

Further, if any one wishes to alienate his share they should sell it to the other co-owners.

in your father lifetime he can execute a registered will in favour of 3 son. during lifetime of your father your bother cannot sell or mortgage said property.

1. You can ask your father make a will with second floor on your name and other floors as per his wish. 

2. Your father  can ask ask tenants to deposit rents in account of respective beneficiaries as per his will. 

- Since, the said property is a self acquired property of your father , then he is having his right to transfer the same to any person , and none can challenge the same legally. 

1. Yes, after getting share by way of registration sale deed , one will have his own right to transfer /sell the same without others consent, 

- You father should execute a Settlement deed with the conditions for not selling the same to third party .

2. As above .

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