I was always told that if someone tells you thier food is kosher and they are knowledgable in halacha, you can trust them.
If you have specific requirements (like CY or Bais Yosef) you can ask the person before hand.
My sister and BIL are more machmir than I am, so when they come I either don’t serve them certain things or preprare it the way they want. There are certain items they don’t eat at other people unless they know the people eat it a certain way. They just don’t make a big deal about it.
Pesach is definately different as there are so many different minhagim and chumras.