Will my parents, uncles, and grandfather be rewarded for donating land to build a mosque, and will a person who donates a small amount of money to build a mosque be rewarded?

Your uncles donating the plot of land they were compensated with to its owner, with the intention that the reward be for their father—a good deed for which they will be recompensed, and its reward will accrue to their deceased father. Whoever did not donate their share will not partake in the reward.

If you are able to build a mosque, you will receive the reward for the entire mosque. If you are unable, then participate in building a mosque, and your reward will be commensurate with your participation.