Is the Hajj valid according to the four schools of thought if the pilgrim performs Hajj al-Tamattu‘ and had a previously invalidated ‘Umrah, and will he be released from his former state of ihram for it by all [schools] after this Hajj, and is it permissible for him to marry?

If we assume you are still in your previous state of ihram (definition), and you went to Mecca, performed Umrah (definition), and then disengaged from ihram, then everything that was forbidden due to ihram, such as marriage, becomes permissible for you. You would not be considered a "mutamatti'" (one performing Tamattu' Hajj) if your initial ihram was before the months of Hajj, even if you disengaged from ihram during the months of Hajj, because the condition for Tamattu' is to enter ihram for Umrah during the months of Hajj. You would also not be considered a mutamatti' if you entered ihram for that Umrah during the months of Hajj in a previous year, because the condition for Tamattu' is to perform Hajj in the same year in which you entered ihram for Umrah.