Can the Rov put forth the rules of a wife following the minhagim of her husband. I.e. The husband follows the view in America to eat/drink cholov stam. May the wife,who had been raised to be stringent and not rely on that opinion, follow her husbands habit. (If yes, would she need to be matir neder). Thank you for always being there!
In general, a wife follows her husband’s customs for all intents and purposes, for for stringencies and for leniencies, and there is no need for hataras nedarim. This principle emerges from a number of responsa in Iggros Moshe (see Orach Chaim 1:159; Even Ha-Ezer 1:58; Rabbi Ovadyah Yosef, in Chazon Ovadyah, writes however that there is a need for hataras nedarim).
Only with regard to issues of hair covering does Rav Moshe write that a husband cannot tell his wife not to wear a sheitel, writing that “this is her halachah” (meaning, that the issue of wearing a sheitel is her ‘personal’ issue, and a husband cannot instruct his wife in this matter). For (almost) any other matters a wife follows her husband’s customs for all purposes.
Therefore, if the husband’s custom is to eat chalav stam, it appears that the wife can follow the custom.
Yet, there is room to argue that in this case, because even those who permit chalav stam (see Iggros Moshe Yoreh De’ah 1:47-48, 35) write that it is preferable to avoid it, the wife’s custom will be considered more halachically ‘correct,’ and she cannot be obligated to follow her husband and eat chalav stam. However, if she wishes she still has the right to follow her husband and be lenient in the matter.
Concerning the general issue of chalav stam, please see https://dinonline.org/2011/02/27/chalav-akum-in-chocolates/.