Hi Patricia -
I am sorry to hear of your recent loss. I am certain that all of ours' prayers are with you.
I am also not an Attorney. For the sake of full disclosure, I am a Certified Professional Landman and occasionally offer up what little information or advice I might be able to provide here on the Forum.
It is always best for me to suggest that you contact an Attorney regarding your questions, so I do so. Most will allow an initial conversation / consultation free of costs.
You mentioned that your Mother-In-Law had a 50% mineral interest, indicating that it was deeded to her, and that her Will had not yet been submitted for probate. Do you have a copy of her Will or have you read it? Who does she leave the mineral interests to?
Also, you refer to the land as "our land". Is this to indicate that your husband left you his share of the mineral rights in his Will and that you and your Brother-In-Law are now the owners of the subject mineral rights?
The reason I ask is that to the best of my knowledge it is not typical that inherited properties automatically pass down to surviving Spouses. Surviving Children, yes. Surviving Spouses, not typically.
Your husband would have had to specifically leave you the mineral interests, inherited by him from his Mother, even if only covered under what is referred to as a "rest and residue" provision in his Will.
They can't lay seismic cables across your land without permission. If they were to lay seismic cables across your neighbor's land and in the course of their seismic research the resulting computer image "bleeds over" under the fence line and shows something about your land, it is my understanding that they cannot research that portion of the image. It's referred to as Mineral Trespass or something similar. You should be able to Google it.
Some States require a certain percentage of participation from the interest owners (a certain percentage of the Mineral Owners in a given tract must sign Seismic Permits), but none that I am aware of presently require 100%. Louisiana tried that and it was a resounding failure.
In other words, the other 50% Interest Owners, or even an Owner of a single 1%, might sign a Seismic Permit, thus allowing the company to include your lands / interests in their research without ever contacting your Brother-In-Law or you.
If you own the surface, you will be reimbursed for damages. Settlements of that sort are typically settled before the Shoot. In a situation like yours, where neither of the subject Wills have been submitted for probate, the seismic company may just have every possible heir sign a Settlement Agreement and cut them all or each a check.
Eastern MT is correct that you can be included in a unit without your title being clear or whether or not you are leased - they pool the land, not the mineral interests.
But since you know they are coming, I assume they must know where you are as well. If and when the Seismic Company or any subsequent Oil and Gas Company reach a point to where they are required to obtain signatures from whomever, they will contact you.
Hope this helps -