See as per the Rules of the EWS, its given that the family at its entire spectra don't have the land greater than the given specifics. So as your grand father is included in your family, then it may influence your eligibility.

It would be better for you to contact a lawyer  and get it discussed. They will give you a more detailed legal overview and it will help you to understand your eligibility. So my opinnion will be that you should consult a lawyer.

The eligibility for the EWS certificate are:

• The annual income of the family of candidate should not exceed 8lakh per annum.
• The family should not hold 5 or more than 5 acres of land.
• The family shouldn't have a residential area more than 1000 sq feet.

I hope this answer helps. All the very best for your future endeavors!