As a 50% owner of my deceased father’s home, do I have the right to have access and use the pool in the backyard?

Hello. If this matter were to be at issue in Minnesota, I would recommend you confer privately with an attorney who will advise you as to your rights. This website provides general information and general principles of law, not legal advice for your particular issue. If I were in your situation, I would confer with an attorney about the matter. I note to you that I urge you not to behave in any inappropriate or disruptive manner such that peace officers (the police) are called. Some attorneys are available seven days for emergency legal needs. Many attorneys will confer initially at no charge. Then, if legal work is performed, some attorneys will provide a reduced fee for financial hardship. Some attorneys may also assist you in limited scope manner to conserve legal costs. All the best.

You don't say who owns the other 50% or if you have already havce or are simply going to inherit your 50% share upon the completion of the probating of your father's estate.  Do widow and boyfriend rent the house?  If so, you have no right to use the pool or anything else without their invite.  If the home is not being rented and, for example, you and widow each own 50%, you have as much right to live there and/or enjoy the amenities, including a pool, as she does.  If you and widow each own 50% and she lives there and you do not, you may be entitled to receive 1/2 the reasonable monthly rental value of the home from her - see a local attorney to help get this all straightened out.  If you and she can not agree to things, in the end it may be that one of you will need to buy the other out or simply both sell the property, each take 1/2 of the net proceeds, and go your separate ways.  Good luck.