Animus Possidendi is included or is it still to be established.

I am in posession of a property since 1996 under an invalid sale deed.I have built ground floor and first floor.Electricity connection was taken in 1997 and Water connection was taken in 1997 and both are in my name. Since the year 2000 the house is assessed for tax and I am paying the taxes also.NO ONE has even spoken a word about my posession which is peaceful, continuous and open. Varada Pillai Vs jeevarathnammal( AIR 1919 PC 44,Bondar Singh Vs Nihar Singh 2003 (8) SCC 729,State of West Bengal Vs The Dalhosie Institute AIR 1970 SC 1778 are all case Laws to the effect posession under an invalid/void document is adverse to the real owner from the inception i.e from the date of the invalid sale deed. Now,I want to file a suit for declaration of title. My sincere request to you all is whether I will succeed in proving that My posession is adverse since 1996? As per the case laws above my posession is adverse since inception because the sale deed is not registered and void in Law. My Question is should I have to establish Animus posessindi separately to establish adverse posession or the above case laws have proved it by stating that my posession is adverse from 1996. Is there any chance that my posession can be viewed as permissive because the vendors have permitted me to be in posession under the sale deed. PLEASE.PLEASE reply.