Obiad means dinner, not lunch.
That's right. We don't rather use word "lunch" in polish. Something similar to lunch is second breakfast - drugie śniadanie.
Can I use lunch or lansz here?
We accept "lunch" in Polish, but "lancz" really doesn't seem common enough.
@LauraELopez: "kolacja" is definitely a common word.
Cześć, and the word 'kolacja' is common or you regularly use another?
Would it change to "wasze rodzice" if you had to female parents?
So you mean two moms? Or rather at least four moms, because "wasze" refers to more than one person? No, not really. Either still "wasi rodzice", but more probably "wasze mamy", so exactly "your moms".
When speaking about siblings, the verb is singular but parents it's plural? Why, Polish, why?
Well, "rodzice" are a simple noun, it's "rodzeństwo" that is special, being neuter and singular, like a mass noun.
Why is "wasze rodzice" incorrect? Hypothetically i could be asking a group of people about their parents and thus use the plural "you"?
There are two plural categories in Polish. Since rodzice belongs to the masculine personal (virile) category, it must be wasi.