I live on a pipestem. In my case, there are 4 houses. Each on its own lot.
A pipestem is usually used when there's an odd land configuration--enough land for the lots, but not really enough for 4 driveways.
The property would be worth slightly less, in most cases. Not a lot. Just a little. Some buyers want their own driveway connecting to the road. They don't want to share a driveway. On the other hand, often the homes are set a bit further back from the road, and if it's a busy or noisy road, being set further back is an advantage.
One drawback (sometimes) is that the homes themselves are kind of clustered together. Where I am, the lots themselves are nice and large, but the 4 houses are each on the nearest corners. So, I've got a nice back and side yard, but very little front yard. The house next to me, facing the street, has a nice, large front yard but almost no side yard.
Again, though, it's called a "pipestem." And it could have a minimal effect on values.
Hope that helps.
One important thing here is to check and see exactly what the easement is for and how long the easement is granted. You can do this by getting a copy of the easement through your title company. This is important because if there isn't a legal easement in place then you could have a house with no legal way of getting to it.
Dorene addresses the less desirable of two situations. Even so, property owner's have a right to access their properties and established easements usually don't pose any serious threat to value that hasn't already been factored in. However, you say the homes are all on one lot? If this is the case then there is no easement and you simply have three units which share a driveway and most tenants are grateful for off street parking..