Ihr seid Frauen = You (guys) are women
Sie sind Frauen = They are women
Sie sind Frauen is also the formal way to say "you are women", while Ihr seid is informal and always plural
So if "Sie sind Frauen" can be both " They are women" and "You are women", how do we know which one is correct?
sie sind Frauen = They are women
Sie sind Frauen = You are women (fml.)
The formal Sie in the sense of you is always capitalized for this reason.
Ihr is a plural of 'you', like the slang "y'all"
Sie in this context translates to 'they'
If you are speaking to a group of people, use "ihr"
If you are speaking about a group of people, use "sie"