My son married a woman who converted to Judaism through the London Beth Din. She now refuses to follow any Jewish practice. Is her conversion still valid? They have a baby boy who is now a year and a half; will he be considered Jewish? By the way she forbids me to have any contact with the child. She is highly unstable and also prevents my son from having any contact with me or his brothers. I am in regular email contact with him. We are a shomer mitzvot family, though I doubt my son keeps anything now.

Let's start with your basic question, is your grandson Jewish? Yes. So far as I am aware, once someone has been converted by a well-respected Beit Din, the conversion holds everywhere regardless of how the person's relationship to Jewish practice changes over time. Any children born to a woman so-converted are absolutely Jewish. Were someone born Jewish to cease following core Jewish practices, we would be still be considered Jewish, too. You don't mention if the parents had your grandson circumcised. Though this has no bearing on whether he is Jewish, he does become responsible for organizing this mitzvah for himself, when he is old enough to do.

Recently I coordinated a meeting with a ChaBaD Rabbi who is a licensed psychotherapist and known to me as a real mensch, with a family that was fracturing along Jewish religious lines due to what looked like the daughter-in-law's extreme religiosity. When we explored the issues involved, it turned out to be mostly about unfilled childhood needs. A healing plan is now in place and this is making all the difference to rebuilding that family's capacity for loving connection, regardless of their individual relationships to religious practice.
 

Please keep in mind that religious practice can vary widely during a life time. I encourage you to avoid showing the kind of aggressive disappointment or coercive threats that will provoke even greater distancing of your family, and your grandson, from you and from their Jewish roots. All is not lost if you have done so, the human capacity for healing is substantial.

To maintain this part of your extended family in your life, it is vital that do your best to be kind and supportive of the couple's secular life. Send appropriate gifts for birthdays. Acknowledge each person's strengths and avoid criticizing weaknesses. Offer financial support if you can afford to, if it is needed. Send photos of yourself at a young age with your own parents, perhaps, in the picture too, send family stories and inquire about photos of your grandson and his parents.

Don't hesitate to extend regular invitations to join you at any time and for Jewish holidays. If rebuffed, don't push the point.  A simple: "Perhaps another time, I/we love and miss you" might increase receptivity over the years. Avoid creating dramas and painful encounters that will long-be remembered and traumatic to you, and to them. If they come and don't dress modestly enough, leave it alone rather than turning that into an issue.

Most frum families have relatives who are not; can each co-exist with the other?  Kindness and accepting each person for who they are and where they are on the journey right now is the path, imho,  to sustainable relationship and personal growth. Trust that your son's feeling for Judaism will gradually be able to return and his wife's Jewish practice spark will return when other family issues resolve in safety. Or, like a vast number of Israelis, perhaps they are content being "just Jewish."
 

Be careful not to override the parents' religious preferences with the child, while at the same time don't abandon who you are and your own Jewish practice. It's fine if your grandson knows about practices from contact with you and perhaps tells friends "grandma has her own dishes at our home and brings her own food when she visits because she keeps kosher and we don't." Your religious life will be a healthy source of curiosity for your grandchild, keep the door of connection open.

Sitting in our china closet here in Philadelphia is my grandfather Benjamin Fradin's blue bowl that he brought over from Eastern Europe. Only he could eat from it, for he used it to eat kosher dairy when he would visit my childhood home. I keep a kosher home, though my mother didn't (save for not bringing in shellfish or pork). Zeyde also had a Shabbat timer in his room for his bedside light, even though the rest of the house didn't. He never sacrificed the integrity of our family for religious practice, we all accommodated each other gracefully, so far as I could tell growing up. When there is a will for the mitzvah of a peaceful family -- shalom bayit, there are many ways to get there.
 

I hope you have a good professional counselor or mashpi'ah. If the situation brings you toxic shame, should it become known where you live, you can also seek hashpa'ah via Skype via an organization like ReclaimingJudaism.org. In the absolute worst case scenario, in the face of a failure of the strategies above, it is sometimes possible under civil law to file for regular visitation time with a grandchild—involved grandparents can be very significant to a healthy upbringing. If the physical distance is great, say another country, regular visits via a service like Skype are a worthy form of connection. 
 

In conclusion, Yes, your daughter-in-law  is Jewish, and your grandchild is Jewish. If you possibly can, refocus on a long-term plan to foster loving family connections. May your process be blessed.