Recommendations of local agents

My two sisters and I have recently inherited ~5 acres of land in Reeves county, and since then we've had two offers, one to buy outright all our royalty rights and one $50 offer for right of way. I am based in London, England, one sister is in PA, and one in Washington State. The estate lawyer (in Washington State) is a probate specialist. He didn't even know that the Texas land office gets 50% of any royalties.

I'm exploring the possibility of having a local Texas landman as an agent, who would deal with this for us, do all the negotiations, paperwork etc, disbursement of royalties etc for a percentage fee. Are any of you in a similar situation or know of a reputable agent that we could contact? Obviously we would want an agent that would be working for us (i.e. the landowners), rather than for gas or oil companies.

In the first instance we need to get the land valued for Washington State Estate tax.

Thanks, Nora Leonard