Yes, there's no problem:)

Yes, you can say so. あれはだれのかばんですか？（Who does this bag belong to? ） あれは私たちのかばんです。（That's ours.） あれは私のかばんです。(That's mine.) あれはぼくたちのかばんです。 (ぼく　can be used for men. meaning the same with 私) あれはぼくのかばんです。

Yes, the first one. Who does this bag belong to? Is it well? Also Does it work with a group a people? I mean Does someone can reply saying "私たちのです"?

does this translate into: who does this bag belong to? whose bag is that? does this bag belong to anyone?