my sons x partner got married she now after seven years she wants him to pay for his child who as her husbands name and thare have two more children

Yes... unless they adopt the kids, child support continues.

Alimony on the other hand WOULD stop.

my sons x partner got married she now after seven years she wants him to pay for his child who as her husbands name and thare have two more children

Sorry! I cannot understand your question.
If he is the father he will have to pay child support.
Her re-marriage and the child's last name do not have any legal matter.

First, She cannot have legally given the child her husband's last name without your son's permission. This is assuming your son was the legal father by being on the birth certificate or a written acknowledgment of paternity.

Second, Unless the husband adopted the child, then the legal father (your son) is responsible for helping to support that child.

Was there no child support order when they split? Has he not being supporting the child the past 7 years?

First, She cannot have legally given the child her husband's last name without your son's permission.

Unless by default:)