Good evening, I am sorry to hear about the discovery of grubs. It sounds like you have already started to do some research about what to do with them, as they can be problematic in this area.  Usually 2 to 3 grubs in a square foot area is not enough to cause problems. It sounds as if you are not sure what may have killed the grass prior to you moving in. It may be beneficial to evaluate if there are other issues impacting the turf as well.  A soil test might be a good way to start. If you believe that grubs were a problem before, it may be ideal to start a preventative program as well. 

White grubs are the larval stage of several insect species including Japanese Beetles, RoseChafers, and May June Bugs.  One article from the extension that gives a lot of detail about lifecycle, as well as treatment can be found at https://extension.umn.edu/yard-and-garden-insects/japanese-beetles#curative-insecticides-1592863.  Preventive insecticide treatments should be applied from late May to early August. Applications after mid-August and in the spring time, when grubs are fully grown, are not effective. One Insecticide available to prevent grubs is GrubGone, but it may take multiple seasons. In August/September apply a curative insecticide to reduce grubs, then focus on preventative.  preventive insecticides (vs curative) are better at reducing the number of grubs.

Please let me know if I can help further.