Do a large number of Sants descend on the earth at a time to liberate the Jivas?

No, this is not necessary. Param Purush gave Niranjan this universe to rule for a period of 17 Asankhya Chaukri Yugas as boon. So all the Jivas are not to be liberated at the same time. That is why the Sants don’t descend on the earth in groups. The universe is not to be made uninhabited and barren. A single lion is enough for a forest. In the same manner, a single Sant is enough to take all the Jivas across the worldly ocean. However, he uses technique to remove the misconceptions of the Jivas and take only those ones to Amarlok who appear to be awakened.
It happens in two ways. Either the Jivas make themselves fit for His grace and recognize the Sant Satguru or the Sants themselves shower their grace on them out of delight.