An interesting note on citrus seeds is that they can and often do produce true to the fruit. One reason for this is that many of them can be pollinated by themselves. Without the need for another tree the seeds have no genetic pollutants.
This is not the case for all citrus however and in these cases you would need two of the same type of citrus growing near each other to increase the chance that the trees grow true to the fruit.
I have successfully grown key limes, kaffir limes, and lemon from seed and they have all grown true as far as I can tell. One reason for this is that orchards usually clump all of one type of citrus together. It would kill production to have them scattered.
I don't know if the kumquats will produce true since the tree had two different orange trees planted right next to it. It might be interesting to see what comes up.