Having recently spent time with my brother and his wife, I observed that the wife frequently asked my brother questions she could easily have asked me. Or she asked my brother to ask me the questions. OK, so it isn’t unreasonable to say “she’s your sister- invite her to come babysit”- but at other times it seems odd and awkward.* And so I ask you, do you feel like your siblings’ spouses speak through them rather than directly to you?
*Odd. Setting: the dinner table. Food served: chicken legs fixed on the grill with BBQ sauce. I picked up my chicken leg and got sauce on my cheek. Niece (aged 2) says “Aunt Eureka, you have something on your face. There’s a big sink over there in the corner” (points to sink in corner of kitchen). (Note: OK, she doesn’t talk quite that clearly, but that was the message understood by the parents.) My sister-in-law laughed so hard she shot jello through her nose. My brother laughed almost as hard. I sat there baffled and a bit embarrassed. Sis-in-law says she laughed so hard because she had observed the sauce, and had planned to tell my brother to tell me that I should visit the bathroom and remove the sauce from my cheek.
Yeah, okay, that’s weird. :dubious: Your sis-in-law is definitely a little bit on the odd side.
In answer to the actual question, nope - I can honestly say that my in-laws (both my brother’s gf and my husband’s sisters & their partners) all speak to me as if I’m an actual real person who can communicate with them, rather than using other people as sock puppets to interact with me. 
I guess I’ll have to start chalking that up as a positive mark for them…
My mom tries this sometimes. My husband will be right there at the table with us and she will ask if he eats some particular food. Ask him, mom. Sheesh.
We can’t understand my sister’s fiance at all. He mutters his words and we can’t make out what he’s saying so he talks and my sister keeps up a running translation.
My maternal grandmother did this with all her kids’ spouses - to the day she died, nobody could figure out why, and Grammy wasn’t tellin’.
A quick note of clarification: It isn’t like my sis-in-law never speaks to me directly. In fact she asked me/ told me things more often than she asked my brother to do so, even when he was in the room. But just often enough to be notable, with me in earshot she asked him a question that would be better asked directly of me.
Next time you’re with them, ask your brother to ask his wife why she never talks to you directly. See if she gets the hint.
Both my brother-in-law and my sister-in-law ring me quite often to chat.