Using Non-Mevushal Wine
My parents keep a kosher home and observe shabbat. This shabbos my parents will be hosting friends who are secular/reform who are are not shomer, but plan to keep this shabbat at my parents home.
In regards to the wine, when people come to shabbat dinner that are not shomer they serve Mevushal. Since these friends will be keeping the shabbat can non Mevushal be served? Albeit, they have not previously kept shabbat or plan to keep shabbat in the future would it not be negatively Judging a Jew because they could have a positive expirence and thus propel them to keep the Shabat in the future?
How many shabbats would a Jew need to keep, to be classified as a Jew who observes shabbat hence could pour non Mevushal wine without issue?