If the property that benefits from an easement is later split into several lots, do all the new owners get to use it?

Generally, yes. Absent wording in the original grant that says otherwise, the resulting lots continue to share the benefit of an appurtenant easement after the dominant property is subdivided, since the easement was created to benefit that land, not just whoever happened to own it as a single parcel at the time. Splitting the dominant property into several new lots doesn't automatically cut off the benefit for the pieces that result.

The real limit is on the burden this places on the servient owner, the property the easement crosses. Courts are alert to situations where subdividing the dominant land meaningfully increases the intensity of use beyond what the servient owner originally agreed to or had established against them, for instance, an easement meant to serve one home now being used by access traffic from several new homes on subdivided lots. That kind of substantial increase in burden can be challenged by the servient owner, even though the easement itself technically still benefits the subdivided land.

Anyone subdividing land that benefits from an existing easement should review the original grant's wording carefully and consider whether the servient owner's consent or a new arrangement is needed, rather than assuming full, unrestricted continued use is automatically guaranteed.