I have a Green card and my mother-in-law would be on a visitor's visa .Can I accompany her in the Visitors line at the port of entry in US . She does not speak or understand English .And we are travelling together
Yes you can. You are traveling together and related by marriage, and you serving as her interpreter will be helpful.
In accordance with 19 CFR 148.34(b) member of a family residing in one household includes all persons who meet the following three conditions: 1. Are related by blood, marriage, or adoption;