Legal Question in Real Estate Law in Massachusetts

You have the same rights as your father. If you are going to refuse to sell, your father can force a sale by seeking a sale by filing a Petition to Partition. ( I assume you are over 18 years old) The realtor will need your agreement to sell the property. The truth is that the realtor made an error in not having you sign the listing agreement and he/she should have all the owners sign a listing agreement. You have the right to know how the property is being marketed and any other questions you might have, You have all the same rights as your father assuming your are an adult and independent (meaning not subject to a guardianship).

You do not say if your father's name is on the deed. If it then the previous answer applied. The realtor is wrong. Any signatures are needed when you sign up with the realtor to list the property, assuming you listed it,

The realtor is wrong and you need an attorney. The sooner both parties understand their rights the sooner they can make the best possible decision about what to do next. The broker is acting unethically and shortsightedly. Maybe the broker will be able to food the buyers on the acceptance of their offer, but when it comes time for the purchase and sale, all owners are going to need to sign. Assuming that you and your father are on the deed to the house, any deed signed by your father to these buyers would not convey good title and, as a practical matter, they will be dead in the water without your cooperation. There are a number of things to consider here, and I recommend having an attorney.