Susan,
There really shouldn’t be an issue with variations in oil quality if all of your wells are producing from the same formation. The only potential downside is an inaccurate allocation based on periodic testing rather than individual tanks for each well. If done carefully, the error won’t be much.
Another benefit to you will be more regularity in your payments. Oil is sold by the truckload and as wells decline in production, a month may go by without enough production to fill a truck so nothing gets sold. With multiple wells producing, you will get checks for your share of the combined production every month.