From one of the Eastern Churches that do not recognize the Pope in Rome as their Pope? What about Sedevacantist and SSPX can they intermarry?
IF, Orthodox deny the papacy, that is the primacy of Peter, and are therefore heretics. The papacy is not the only Church teaching they deny. They reject all Catholic Church teaching since they separated themselves from the true Church, eg the Immaculate Conception.
It would not be very unwise to make such a marriage.
Sedevacantists do not deny the papacy. Sedevacantists accept all the truths taught by the Catholic Church. A sede and an SSPXer would have a few things to sort out, but all couples considering marriage do, on all sorts of things.
Two very different situations. That's my 2c.