I want to say that it is too much, indeed having two accounts is an offense for casinos that prohibit it, but this should be a clear concern if talking about the IP that is used the same, this is not just about the family, what if using public wifi at work, in cafes and in other places then using the same site, will it be labeled as an alt account, of course this is not something that should be responded to by closing accounts and so on that harm consumers.
That's why the first step any gambler should take before registering at any casino is to read the terms or services extensively. These days the document is not as bulky as it was a few years ago. It is now written simply and understandably. There was an issue where students of a university shared the same internet connections and their accounts were restricted. The students were only allowed to use the school's wifi and it became a problem. I think it is high time casinos should start seeking other advanced means of identifying multi-accounting. These students had to be subjected to stringent KYC processes for them to prove innocence.