Divorced birth mother is now married to the bio father (DNA proof).
Ex husband is on the birth certificate of the child and he is the legal father with rights, under Michigan family law, while the bio father has none.
The mother is fighting legally to revoke paternity rights of the legal father. Both birth parents are married to each other and live with their child happily. The legal father forces visitation and contact with the 2 year old child having the legal right.
He insists to be part and interferes in the life of this normal and natural family, pretending that he loves the child although the reality is that he is acting out of Revenge, as he openly admits that he cannot forgive her.
Any such case anywhere in the US?

I can't quote any cases, but can easily believe that it happens more than you seem to think.
Bottom line is the law. The REAL bottom line is the child's peace of mind.
The mother has to realize that she had the ex sign the birth certificate, regardless of the reason (knowing or not knowing is no excuse), so she has to accept equal responsibility for their actions, and that includes allowing him visitation until and unless the Court says otherwise.

Bio parents need to get to court and handle their business properly and straighten this mess out. When did they get together after the divorce? This sounds like the consequence of cheating to be honest.

As the legal father he does have the right to visitation that the judge ordered. If the bio parents are wanting this to change then they need to petition the court for a DNA test to modify the birth certificate. Right now it doesn't really matter why the legal father is using his rights. They are his rights until changed in court. I would advise acting quickly because there are statutes of limitations for paternity challenges. The last I saw Michigan was three years. I'm not in Michigan so it could be longer but for safety's sake get the petition drawn up tomorrow. Or start calling attorneys tomorrow because it will be a few days before they can get you in if you are wanting to go that route.

You have mentioned DNA proof. What kind of DNA proof do you have? Was it court ordered? If not, was it at least done at a court approved location? If no again, it is useless in court.

The legal father may not have signed the birth certificate, probably didn't. The law in all states makes the husband the legal father by default.


He insists to be part and interferes in the life of this normal and natural family

Excuse me, but the mother caused most of this, not the husband who had every reason to expect the child was his. She interfered with the normal and natural family she had. I don't blame him for not wanting to forgive. Did it ever occur to you that he bonded with the child? Even though it became known to him that the child was not his natural offspring, that doesn't mean he doesn't care for the child.

The bottom line here is that there are laws to deal with this. The law provides for a way for the bio parent to fight for paternity. But there are restrictions. If MI law is not allowing the bio father to gain legal paternity and leaving the legal father with his rights as the legal father, then the now married couple has to deal with it. Again, they caused this, not the former husband. The injustice here was done to the former husband not by him.

Let me see the legal father, who was there to raise a child, when the other father did not. He may have loved the child and wants visits. It seems he is trying to be a good father. He is not disturbing anyone live, he is just asking for the rights to see and visit a child he was raising.

The problem is that the legal husband may keep his rights, it all depends on court.

The bio mother will need to try to hire an attorney who can go to court and try.