A good thing about introducing new characters (or even "new" characters) to an established adventuring party is that the GM can pre-feed them with some story information, which they can then reveal to the group. This gives a more natural feel to what may come across as an infodump if it comes directly from the GM or an NPC.
Commentary by Keybounce (who has not seen the movie)
So previously, I had asked some questions about "Why?"
Now we see. Why tractor instead of radio? Perfectly good reason. And Wedge is still around.
Well, Han and Chewie are still around. Pretty sure Luke could be - everyone is looking for him. Heck, if the rest of the gang shows up, we can bet that Princess will as well. And, of course, Wedge, as a shape shifter, could be anyone. Are we certain this is Chewie?
It's interesting that we come to this now. Another comic I read, Friendship is Dragons, has just gone to the Changeling fight at the Royal Wedding in My Little Pony. Imagine, if you will, finding yourself facing a dozen copies of you. What would you do?
Well, how about hide in the group, and confuse the GM to the point that the GM is moving you into position to attack your friend, and you do a sneak attack on the others.
This is what shapeshifters, form-copiers, can do. You cannot tell who is who you think or not. And in swarms, that can work both ways.
But in singletons? We know that there are other shapeshifters. Heck, we know that there's advanced genetics and cloning. Heck, we even know that the Darths & Droids universe has improv theater to teach these clones how to behave properly.
So how do we know this is Chewie, and not an impostor? Heck, how do we know this is Han and not an impostor? Even Rey is suspicious by the end of this page.
So what could possibly be a test for Han being Han? There's always the Naruto test from the Forest of Death arc. :-)
Commentary by memnarch (who has not seen the movie)
Xasha is definitely being suspiciously reasonable here. This is either a sign something big really is going on (possibly related to Poe's capture or the hunt for Ahch-To's archives) or it's a double reverse Maxwell Smart thing in case Rey was captured and brainwashed while on the mission to retrieve the hyperdrive modulator. If the Resistance knows about or suspects Kylo Ren being able to mind control people however, that actually makes sense as an intelligent move. And if it turns out that there is something big going down and an evacuation is actually going on, then family members warning each other makes perfect sense.
In spite of all the crazy things Han did, he did have the occasional great idea. Not to mention successfully playing a traitor four times without getting caught or turned out by either side; that takes skill. On the other hand though, Han was never that particularly cautious and looked like he would usually try to bluff or fight instead of plotting and planning beforehand. I bet Chewbacca came up with the idea of tractor beaming them into the freighter versus broadcasting a message the First Order might overhear and need bluffing against.
Hmmm. I wonder if there's a lot more to the First Order than just the Finalizer we've seen so far. Space is big. Really big. And while active energy sources would be relatively easy to spot up close, the distances involved in space would mean crazy amounts of luck would be needed to be successful with passive scanning. To have active scanning be reasonably successful, the First Order would need either lots of energy to broadcast the Black Alpha signals (radiation type?) or lots and lots of ships. Given that we just found out that the First Order is working for Nute the sentient computer virus, I'm betting there's lots and lots of ships involved.
Xasha: We’re here to warn you not to go back to the Resistance base.
Finn: Why tractor beam us instead of using radio?
Chewbacca: We picked up Black Alpha signals.
Chewbacca: The First Order were scanning the whole Tatooine system. We had to get you inside the tractor beam immediately.
Chewbacca: With any luck they’ll only have seen an old bulk freighter, and assume you must have jumped out-system already.
Rey: What’s up at the Resistance base?
Xasha: Wedge brought in some intel about a planned First Order strike. Something big.
Chewbacca: We don’t know where, but we have to assume the base may be compromised.
Xasha: Evacuation has begun, but it’ll take a while. We didn’t want you showing up just before it gets attacked.
Rey: All this sounds very reasonable. Who are you and what have you done with my real father?
Chewbacca: Ironically, that line works less well on a serial identity thief.