There are issurim midoraisah in insulting others, and there are kullas for chalav Stam that can be used to avoid this situation.
There are two factors at play.
1. In someone else’s home, someone who is shomer shabbos and kashrus, you can generally rely on their standard. I have asked this Shayla many times about different situations such as work friends, family, etc and this is the answer I received. However, if you know for a fact that there are issues, ask your local hallachik authority.
2. The kashrus of chalav Stam is another issue. If you hold that it is pashut treif, and you are eating hot cooked food with their utensils, ask a Shayla. From what I have seen, the plan is not noheig like this. They hold chalav yisrael as a chumra, not as an ikkar hallacha.