1) if the will of 1989 had been genuine your siblings would not have agreed to conveyance being executed in favour of you and your siblings
3) your siblings would have relied on the will to have the house mutated in their names as per the will
3) the fact that for period of 26 years your siblings did not rely upon will casts doubt about the genuineness of the will
4) file suit for partition to claim your share in house as per conveyance deed