Both have same meanings but "it is ours" means that "they" feel more reluctant to give what belongs to them" rather than "it is from us". I think this verse depend on the situation? Please cmiiw
"ons" would then translate to "us" ("It is us"). "is van ons" practically means "belongs to us", which we shorten to "is ours".
Yes you use "onze" with de-nouns, and "ons" with het-nouns. And know that we use "onze" with all plural nouns ( de and het )
"It is from us" in English suggests that it is being given from us to someone else. "It Is ours" is possessive and there is not transfer of possessionto someone else. If you say"Het is van ons" in Dutch canthat be use in eithr situation.