What should a mourner do if he arrives at the cemetery to attend multiple funerals for people he doesn't know, especially if there is a large number of them?

The number of qirats multiplies with the number of funerals. Whoever prays over a funeral receives one qirat, and whoever follows it until it is buried receives two qirats. There is no difference whether this occurs all at once or in stages. This is from the bounty of Allah Almighty.