Which Czech word are you asking about?
1. muže - masculine singular accusative
2. vašeho - masculine singular accusative
3. známe - first person plural
Are you asking why "vašeho" instead of "tvého"? That is the difference between "polite you" and "familar you".
The word "váš" can be plural as well as singular polite. But the masculine accusative plural is then "vaše", not "vašeho". The latter is singular polite only.
I might be misunderstanding your question, in light of other responses, but "second person plural" is a verb-related term. The verb in this sentence (známe - we know) is first person plural. The object (vašeho muže - your husband) is a singular masculine animate noun in the accusative case, along with the "matching" personal pronoun.
Hope this is helpful... if not to you, maybe to someone else who comes along! :-)