If I use iCloud on a laptop to view texts/emails/web activity in somebody's iPhone, will they know?

If I use iCloud on a laptop to view texts/emails/web activity in somebody's iPhone, will they know?

As long as they don't have two factor authentication enabled and that laptop has been used to sign into the iCloud account before then no.

If they have two factor autehtnication enabled then you won't be able to login without a code which would show up on their phone meaning they'd know about it. Also, if they don't have it enabled but that laptop/location has never been used to sign into the account before then they would receive an email about it

If you don't own the account and don't have permission to use it, you're breaking the law.

Yes.