Can a sefaradic eat non Beit Yousef meat in the house of an ashkenazi? like if he is the guest?

Shalom, Thank you for your question. There are differences between the halachic rulings of the Shulchan Aruch and the Rema in the question of "glatt" or "chalak" meat. The Shulchan Aruch holds that if the lungs of the cow were not completely smooth, ("glatt" in Yiddish, or "chalak" in Hebrew) the meat is forbidden. The sephardic community follows this ruling. The ashkenazi community holds that if there was an adhesion to the lungs which could be removed to show that the lung was smooth underneath the adhesions, it is kosher – but not "glatt". There is another difference between the opinions, which is that the Rema (who the ashkenazim follow) considers that a small, easily removable adhesion is defined as a lower class of adhesion, known as "rir", and that the presence of up to two such small, easily removable adhesions still qualifies the animal as glatt according to ashkenazic tradition. The sephardim, according to the Shulchan Aruch, forbid even this lower class adhesion. Based on this, it would seem that a sephardi Jew should not eat meat slaughtered according to the ashkenazi leniency. [In truth many ashkenazim are strict and also only use "glatt" meat. Today, the OU (and most other kashrut organizations in the U.S.) will only certify meat that is glatt, albeit not necessarily glatt Beit Yosef.] And this seems to be the custom, that sephardi Jews make sure to buy their meat with a sephardi "Bet-Yosef" standard supervision. However, when it comes to eating meat in an ashkenazi house or function there is room to be lenient. Rav Ovadya Yosef shlitah quotes the responsa of the D'var Shmuel (of Rabbi Shmuel Abuhav zt"l, from Italy around 400 years ago) who allowed a sephardi to eat from ashkenazi meat as long as it was not known for certain that there was in fact an adhesion on the lungs of the cow. All meat that has an ashkenazi supervision on it may in fact have come from a cow that had perfectly smooth lungs, and was in truth "glatt" or "chalak" – such meat would certainly be acceptable to the supervising rabbi. Nonetheless it would be packaged and sold as "ashkenazi – non-glatt" meat because that is the kashrut supervision under which it was slaughtered, and not because it was in fact not "glatt". Because of this doubt [together with the fact that the Rema allows even non-glatt meat] he allowed eating of such meat. Rav Ovadya Yosef himself agrees with this ruling and allows a guest to partake of their host's food (and those who want to be strict should be blessed), all the more so if it is a "mitzvah meal" such as a wedding etc. In my humble opinion, one should certainly rely on this lenient opinion if being strict might lead to insulting someone, or cause tension etc. In such a case, one should rather try to be strict with the mitzvah of loving one's fellow Jew. Blessings.