I believe some (if not most) of the schools has a question in the application form asking whether you have a spouse who is applying with you or is a student at the school.
And you can by all means bring it up in passing in an essay so long as there's an appropriate place to do so - and if you do, it's likely to be a brief reference (i.e. some essay talking about your personal background or about how you'll fit into the school, etc.).
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