Legal Question in Real Estate Law in California

You may have to file suit and restraining order if they do not cooperate. Yes a survey needs to be done as well as review of sale documents: the former owner may need to be joined.

First, disputes between neighbors deserve especial efforts to resolve through negotiation and discussion before going to court. Exercising and enforcing legal rights against someone who lives next door and you're going to be seeing all the time can be pretty uncomfortable, and winning may feel like losing after awhile. I'd advise at least considering having a talk with the neighbor as to why a fence is suddenly in his plans, and whether it could wait until the boundary line issue is finally and fully resolved. If the fence is built in the wrong place, a court is likely to order it be removed.

Next, in considering your options, I'd include looking at whether the seller or seller's agent may have misrepresented anything, such as where the property line is, or its square footage. The neighbor may be right. Your seller might be wrong.

As to hiring your own surveyor, I'd think this would be a good expenditure only if you have some reason to doubt the accuracy of the neighbor's survey, but I'd suggest trying to get the results directly from the surveyor rather than depending entirely upon what the neighbor says his survey shows. Don't rely just on some stakes in the ground; ask the guy who pounded them in what they show.

If the driveway turns out to be partly on the neighbor's property, you have some additional alternatives. These include negotiating a lot-line adjustment, or an easement, or having a contractor re-route the driveway so that it's entirely on your own property.

Finally, to give you an answer to your second question (re how to stop the fence building project temporarily), in addition to negotiating a pause until the survey and negotiations for an easement or lot-line adjustment are complete, you could go to court and seek a temporary restraining order and a preliminary injunction until the court determined where the prooperty line is, and any related issues. This could be expensive and permanently damaging to neighborly relations, and you might lose.....but yes, it's a possibility.