Hello Goinaz and welcome to the Cow Audio Forum.
As I say in my book, "When do you listen? Always!"
House XLR levels may vary from mic to line level or anywhere in between. The operator may not know. As you suggest, yes, you can run the audio from the house through a mixer before the camera. I do that a lot at event where I take a house feed so I can make sure Of what's actually going to the camera and can adjust on the fly, but..........you need someone from you team looking at levels and actually listening to that audio....always.
Regards,
Ty Ford
Audio Forum Leader
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