1. No. His share doesn't get automatically devolved upon co-owners. He's incompetent to contract. He can't give valid consent; that doesn't mean he doesn't have interest. 
2. However, as already stated; he's incompetent to contract. So a guardian has to be appointed for him under Court orders, who will enter into contracts on his behalf. 
3. To file the guardiandhip petition, you have to visit me for exhaustive consultation regarding this. I'm based in Navi Mumbai/Mumbai just as you are. So it shouldn't be difficult for you to pay me a visit. ९८२०८०७८८४.

You need to apply district court to appoint one person as manager to the estate of the mental disabled person who can act on behalf of that person. 

1. If he expires intestate; 50% of his share will devolve upon his wife (your mom) and the remaining 50% will devolve equally upon all his children. 
2. However, if he has already made a Will, the word of Will will operate. 
3. He cannot Will now, as he's incompetent

On father demise his 50 per cent share in property would devolve on your mother and you 

2) ason date you have no share in property 

3) for sale of property your mother can apply to court for being appointed as his guardian and seek court permission for sale of property 

NO till he is alive, but due to his mental incapacity, mother can file application in court to appoint her his guardian than she can sell his share to manage his medical and other expanses for his benefit.

Wife, children and his mother are class I heirs, his share will inherit in them equally. IF his mother not alive than in both of you.

obtain a certificate from competent medical authority to issue a certificate of his unsoundness.

Chief medical officer can issue such certificate.

if your father has any other Class-I legal heir then there consent/no objection will also be required for disposing off the father's propert.

if your father has died intestate, i.e. without leaving a Will, then the distribution of property is done in accordance with the personal laws.

the property share will devolve amongst all legal heir. So in case your father did not have a Will, you, your mother and other siblings will be legal heir and the share will devolve amongst all legal heirs equally. 

if your father has died intestate, i.e. without leaving a Will, then the distribution of property is done in accordance with the personal laws.

the property share will devolve amongst all legal heir. So in case your father did not have a Will, you, your mother and other siblings will be legal heir and the share will devolve amongst all legal heirs equally. 

See in his life he is owner of share but he cannot transfer same, so your or your mother can apply for legal guardian before court and can transfer his share. After the court order you can transfer sale the property.

The share shall be devolved equally in all legal heirs.

1.  Property belongs in 33.33% to the present Three Joint Owners.

2.  On demise of Father, "ALL" the residual legal heirs (including two co-owners) shall be entitled to EQUAL share of the Father share i.e. from 33.33 of Fathers property.

3.  The whole property can be sold even today, by executing a Sale Deed. For this you would require to apply to the local Registrar of Sub-Assurances for a House Visit (by paying statutory fees), who would come to the house, wherein the present Three co-owners would have to sign before him.  A Medical Certificate of a Hospital would be required with the Application.

In case where one co-owner lost his memory due to some disease like alzheimer and other co-owners want to sell the property then they have to file a petition in court for appointment of guardian to sell his share if they are the legal heirs of that co-owner.

otherwise legal heirs of that co-owner can file petition for permission from court to sell the property or transfer his share on name of legal heirs. 

It will go you his class one heirs

1. As per the information mentioned in the present query, makes it clear that the property is jointly owned by you all three.
2. Yes, as the health of your father is not good and that is also the illness in which he can’t really respond to people by understanding the good and bad about the talk, you should get the property sold by making POA on his behalf supported by medical condition.
3. As otherwise, if he dies intestate (as he can’t execute the will) then the property will go to all legal heirs of class I and that may bring people into picture to whom you don’t share such relation.