Without knowing what questions you are referring to, first consider if we should be sending valid questions/users off to another site.
Respect the community — your own, and others’
But on a technical note, it is not possible to close a question as a duplicate of one on another site. Migration paths are not added until a site becomes a lot more established, so if a question truly belongs somewhere else, you can 'flag' it for Moderator attention. But even then, migrations are fraught with problems so we don't generally recommend them anymore.
Migrations are used sometimes (rarelyshould be rarely) to preserve long-standing content. But if the author simply asked a question on the wrong site, you canshould politely ask them to re-post their questions in the context of the correct site.
But posts sent off to another site the author did not intend means losing theremoving everyone's reputation earned by all the authors on this sitethat goes with it, and orphaned posts are often greyed out as anonymous when the authors don't have an account on the target site. You also end up with odd-looking comments that don't make sensequite fit, and often the posts/voting may not fit tone and posting convention of the target site. So generally speaking, migrations do not work that well, so they are generally not recommended as a routine way to shuffle questions off to another site.