Hi. My son estranged himself from my wife and I over two and half years ago, without giving us any feasible reasons.
I don't know what you think the term "feasible" could possibly mean.
It certainly does not mean "...reasons acceptable to
you".
Is he legally allowed to do this...
Yes.
...or can the family law court help us get visitations rights
Maybe.
It can help to understand that you as a grandparent
don't have any rights of the kind you might be thinking about.
In Family Law, rights, so far as they exist, accrue to the child(ren).
Not to the parents, grandparents or other rellos.
So, while the children certainly do have a right to know and have a relationship with their extended family,
that's only available where it's in the best interest of the child to do so.
The Court decides that.
So, yes, you can make an application for a Parenting Order that gives you (some, conditional) contact with the children.
But you don't have any
right to that contact.
You need formal, case specific legal advice.
You'll be paying for that. Yourself.