Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
It is not your duty to pay Zakah on your portion of the real estate that you inherited from your grandmother, since it is a fixed assets. In addition, fixed assets are not subject to Zakah since they are undeveloping properties unless they are a form of merchandise. Then, such assets will be subject to Zakah at the same rate as articles of merchandise. Moreover, if such real estate is rented, then the revenue of its monthly rent is subject to Zakah provided that:
1) Such a revenue reaches the value of Nisaab (the value of 85 grams of gold).
2) Such a revenue should be possessed by one for a complete lunar year.
Here, we draw your attention to the fact that if the house that you inherited was sold before and your share constituted a Nisaab, then you should pay the Zakah for all passed years after selling, whether you took your share or not, taking into consideration the above-two conditions (1, 2).
Also, know that Zakah is obligatory on any amount of money you have, since it is a developing property, but as mentioned above in conditions 1 and 2. Concerning the Nisaab and Hawl. The rate of Zakah is 2.5 percentage.
Allah knows best.