Is a contract signed by four people and not notarized a legal and binding contract?

A written contract is binding whether or not it is notarized. Notarization is mainly for recording documents (like a deed or mortgage) or in the case of wills, trusts, etc.

The value of a Notary Public witnessing a document, is just that, being a third party witness to an agreement between the signing parties. An agreement does not need to be witnessed by a notary public for it to be a valid and binding agreement. If a party is in default of the agreement, you should send that party a written notice of default of that provision of the agreement with an opportunity to cure the default within X number of days (e.g. 5) from the receipt of the notice (send it registered, return receipt requested). If they do not respond within the allotted time, they are in permanent default. As a further step, you should file a petition with the courts to quiet title in the name of the three remaining owners to prevent the defaulted owner from claiming ownership later on. You will file the quiet title order with the register of deeds in the county where the property is found.

A contract does not need to be notarized to be valid. Oral contracts can be valid and so written ones can be too. Of course, there are many defenses to written contracts, but notarization of signatures is not necessary to create a valid and binding?contract.

Notaries are not required for 99% of contracts. Certain documents such as wills need to be notarized. This agreement does not need a notary and is enforceable as long as all parties signed it and it is enforceable under state contract rules.