If your mother is not incapacitated, she could execute a "ladybird" deed under which she deeds the property to your sister while retaining a life estate and the ability to change the deed at anytime prior to her death. To protect against her becoming incapacitated and unable to make necessary changes in the title she should could execute a durable power of attorney appointing someone else (perhaps another sibling) as attorney-in-fact. Both documents should be prepared by an attorney after...
The important first step is to confirm that your grandmother was the sole owner of the property prior to her death. If this was the case, your brother, as personal representative, is the only one who can legally convey the property, and then only in compliance with Michigan statutes. If someone else has attempted to do so, the deed is ineffective, but still likely to confuse. Your brother needs to obtain the help of a real estate/probate attorney to sort this out. The taxes need to be paid....
If the funds are not in a trust, the only issue is whether your mother is competent. If she is, she can't be stopped from making bad decisions, although repeatedly making bad decisions could be cited as evidence of incompetence. You should discuss the matter in detail with a Michigan attorney familiar with elder law, but the fact that neither you nor your sister live nearby is going to make it extremely difficult for you to successfully intervene in this situation.
The corporation can issue shares to you in exchange for your membership interest in the LLC or the corporation can issue shares to the LLC in exchange for its net assets. Either way the transaction needs to be properly documented. I urge you to consult a business attorney.
Unless your father's friend in incompetent, your only alternative is to try to continue to work with her to preserve the property - perhaps by buying it from her if she needs money. If she is competent, she has the right to change her will and leave everything she received from your father to someone other than your brother and yourself. Discuss the matter with an estate planning attorney in your area.
Estate planning is a good idea, but to assure that your wife will have an interest in the property, the easiest thing to do would be to do would be to quit claim the property to you and her husband and wife. There may be reasons why you don't want to do this, which is why consultation with an attorney is a good idea, but if there are no reasons against, a quit claim deed can be prepared, signed and recorded in short order.
The requirements for obtaining title to property by adverse possession do not include advertising. You must actually occupy the disputed property in a way that is visible, open, notorious, exclusive, continuous, and uninterrupted as well as hostile to the tile of the true owner continuously for a period of 15 years. If you wish to pursue such a claim, you should consult with a real estate attorney.