Also we have a large umbrella policy that covers all of our houses.We also own two separate LLCs - a transport company and an espresso stand. 

Also, do insurance companies offer umbrella (blanket) insurance policy for multi-state properties?

I have heard of investor/agents marketing wholetail deals on the MLS prior to taking title which, in my opinion, could lean towards falling under the umbrella of a net listing.Contrast assignments, at least the way I intend to assign contracts, should not allow for the sale price to be driven up any higher than purchase price agreed upon between me and the seller.

We have one corporation that owns all four buildings and individual insurance policies against each property as well as a corporate $2 million umbrella.

If you decide to purchase, conventional financing, backed by Fannie Mae and Freddie Mac require the property to be in your personal name, so an umbrella policy would be worth looking into.

I had thought I'd use a personal umbrella to cover the properties and my personal auto and house rental (don't own my home) but I'm thinking that is overkill as the properties will be well covered by the liability. 

All I know is that the subject of LLC's is almost always mentioned in the context of aiding in LIMITING ones LIABILITIES (against being personally sued), whereas others have said that umbrella Property Insurance should suffice if your personal net worth is not exponentially greater than the value of your individual property.

I can't seem to find an insurance carrier to give me an umbrella policy that covers properties in different LLCs.

The policy is per property address, so if you hold more than one ... you need more policies.It might be good to compare an Umbrella Policy vs Landlord liability coverage.Why such high liability coverage? 

If you want to mitigate risk, I would get an umbrella insurance policy.