Since you have not given any permission to give premises on rent to sub tenant issue notice to tenant and sub tenant to vacate property 

if they refuse file suit for eviction 

You reside in the property of trust as tenant. You rented one room to third party and the tenant in turn rented the room again that fourth person. Maharashtra Rent Control Act, is not applicable to Trust Properties. You can seek eviction of fourth tenant on the ground that you gave him premises free only for some time and now you want to take the rook back from him. You cannot claim that he is your tenant as you are not authorized to rent the room which  is owned by the Trust and you are not a landlord. You have to file a civil suit in the Court adding trust as second party.

Yes you can file a suit as aforesaid for eviction

You first issue a legal eviction notice to the person who is occupying this proeprty illegally under some other name and also to the actual sub tenant.

After that you can plan to approach couirt provided that you were permitted by the original lessor to sub let the leased property.

If original lessor had not authorised you to sub let the leased out property to a third party then your act of sub letting the property itself is an illegal act. 

your grandfather is actually the tenant 

and your GF's tenant is the sub-tenant of the premises

however it seems the landlord trust has not objected against this subletting

so your GF has to file an eviction suit against his tenant in the small cause court on the grounds of non-user for the purpose for which the premises were let, unauthorised conversion to commercial user, bonafide requirement

you have to first issue a legal notice to the GF's tenant and the tenant's tenant 

as the tenant's tenant was paying rent on behalf of the main tenant, he may take a defense that he is the authorised sub-tenant claiming under your GF. In that event you have to state in your legal notice and in the suit that if the tenant's tenant is also claiming tenancy from your GF, then his tenancy is also terminated 

however your GF as the landlord can feign ignorance of the fact that the tenant's tenant was actually paying the rent and that your GF was under the impression that his tenant was paying the rent. Thus you can also invoke an additional ground of illegal sub-letting against the GF's tenant 

1. To get back possession, you have to make both the tenant and subletee parties to your suit for eviction 
2. If the tenant isn't made a party,  there's every likelihood of he filing a caveat as he isn't a trespasser but a lawful tenant. This will only prolong your litigation, frustrating your attempt to get back possession. 
3. You obviously do require services of a competent counsel for the litigation. I'm willing to handle your case as your counsel. However, I require an exhaustive consultation session with you first. You need to visit me for that. 
4. I'm based in Mumbai /NaviMumbai just as you are. So it shouldn't be much difficult for you to visit me for exhaustive consultation. 
5. ९८२०८९७८८४. (Nine eight two zero eight nine seven eight eight four) 

- Since your grand father had given some portion to a tenant , then that tenant cannot sublet the tenanted premises to anyone without taking the consent of your grandfather .

- Hence as the said subtenant is without getting permission from your grandfather , then legally his position is just like as a trespasser. 

- You can file a complaint before the police against him for the offence of trespass in the property , and further if no response then you can file a complaint before the magistrate. 

- Further, you can also file a Mandatory injunction suit also for evicting him from the tenanted premises. However before filing the suit , you can issue a legal notice to him. 

Dear Sir / Ma'am,

Since the house was sublet by your tenant without your prior knowledge, you can issue a legal notice against them to vacate your property. In case this does not work you can file an eviction suit against them.

Thank You.

Your query is not clear 

registration of rental agreement is mandatory in mahrashtra 

Landlord can evict you if you have rented premises to sub tenant without his consent 

Need to study the entire agreement and check the same

Dear sir/ Ma'am, 

we need to analyze your agreement to know if it can get affected by the judgement or not. 

Thank you

The judgment in your favor ws not challenged neither the opposite party preferred an appeal against it, hence that judgment will still be considered as valid and effective.

If you face any problem you can produce the judgment, let the rival party initiate legal action which can be challenged as per law. 

- Since, High court has passed judgment in 1940 , then after the amendment even it is legally valid , and specially when it was not challenged by the opposite party.