It was nice of them to send you an email documenting their hostility and untrustworthiness. They also aren't terribly familiar with the law.
Generally, grandparents' rights are a matter of parental choice. Courts get involved in cases where grandparents have held custody of a child for a period of time, or where one parent is deceased and the surviving parent denies contact with grandparents.
Consulting a lawyer to be certain of the law in your state would be a good thing to do. You should keep any letters and emails to document the situation should they ever find a lawyer who will take the case to court. It probably wouldn't hurt to cut off all contact. Read their emails in case they contain anything you need to be aware of (threats of violence, for example), but don't write back. Change your phone number if you can, use caller ID and don't answer when they call. If they have access to your residence, change your locks.
ETA: This site has information in re. grandparents' rights in MN, where you say your child's grandparents are: http://www.nvo.com/beaulier/grandparentsandvisitation/
I'm not a lawyer, but from what I see here, there is no reason for your parents to believe that they have any right to visitation if you choose not to allow it. Unless they have had custody of your child, they have no legal standing.
It was a little harder to find online infor for CA from a source that looked trustworthy to me. However, I did find a blog on family law in CA (it's here: http://www.californiafamilylawblog.c...hr_1.html#more
) that states
|California Family Code let’s grandparents file for visitation:
· If one of the child’s parents has died.
· If the grandchild’s parents are no married, separated, or divorced.
· During custody proceedings.
· If the child is not living with either parent.
· There must be a pre-established grandparent-grandchild relationship.
· Visits cannot get in the way of a parent’s own visitations.
· Visits must be in the best interest of the grandchild.
Again, it won't hurt to consult a lawyer, but it looks to me like you're in the clear.