Can one be yotzei from a kiddush or hamotzei made by someone who is not always shomer Shabbos?
He goes to a very modern open orthodox shul, but is not so knowledgeable. He keeps Shabbos minimally, but probably doesn’t really keep Shabbos properly or know what that even means. I think he has enumah in Hashem, but his shabbos observance is not a priority. If he had a conference to attend on Shabbos, he would. He would be mechale shabbos in public, but no one there would know he is shomer shabbos at all as he only wears a kippah to shul. I am bringing my own food.
It depends how bad of a mechalel shabbos he is. If he is mechalal shabbos only in front of people that don’t recognize him as a religious Jew, then you can be yotza with his Kiddush and havdalah. However if he would be mechalel shabbos in front of a religious Rabbi then you can not be yotza with his Kiddush.
If he is the more severe type of mechalel shabbos, here are your options. You can either say that you like making your own kiddush or say kiddush together with the host, and then drink from the wine (Note: Both of these ideas will only help if the wine is mevushal or pasteurized). Another option would be to make your own kiddush on the bread that you will eat. The way to do it is the following. After kiddush wash quickly, and while others are washing say kiddush quietly while the others are washing their hands, when you get to the bracha of hagofen say hamotzei instead. Then, when you get your piece of challah that will serve as your Kiddush.
Regarding havdalah, it is a little different, because we cannot havdalah on bread. You can say “Boruch hamavdil…” and do melacha, and make havdalah when you get home. Just make sure not to eat anything before actually saying havdalah.
Ohr L’tzion 20-5, Shulchan Shlomo 273 ftnt 6, Divrei Sofer 1-8, Avnei Yoshpe 3-36, O:CH 296-2, Poskim.