The title says it all

You an add them via console. They won't have banter and dialogue but besides that they will work just fine.

You can also use ManageParty before the cinematic scene, that way you can keep them alive. Or you can recreate them again at the next inn...  (it makes no difference because they have no interactions).

It breaks immersion Calisca's sister if you care about that. Otherwise she is nothing but a poor man's Eder without dialogue.

I meant a mod that adds appropriate dialogue, etc.

No