Hmm, I've never heard of patronymics turning into middle names. To my understanding these 2 are different things that exist as unique cultural entities to all involved, so it'd make no sense to mix them up. Patrominics just get dropped for Russians and only ever matter to them personally, but not officially.

As for a mixed couple that live in Russia. Yes, their children will receive patronymics derived from their father's name. If anything, that information is required to get properly registered as a citizen. There are exception to it though, various peoples that haven't historically developed a custom of giving a patronymic can request no patronymic name. I'm not sure if it extends to a mixed couple, where the father belongs to such a people. In depth examination of the law is needed here, but it looks logical to allow this.

As for a Russian couple in a "western" (never liked the term) country, well, see above. Patronymic would most likely only exist for them.