Catholic Encyclopedia Definition of Mixed Marriages...
(Latin: Matrimonia mixta )
"Technically, mixed marriages are those between Catholics and non-Catholics, when the latter have been baptized in some Christian sect. The term is also frequently employed to designate unions between Catholics and infidels. From the very beginning of its existence the Church of Christ has been opposed to such unions."
The SSPX have recently become much more friendly with those at the novus ordo, and visa versa. So, they probably would not have too much concern about their groups intermarrying. The SSPX don't like the novus ordo, but most of them don't seem to claim that it is likely invalid or should absolutely be avoided.
However, the "Resistance" is quite a bit more against the novus ordo. My pastor has told me that I should treat the novus ordo services like Protestant services. For, even in the case that they are valid, they are generally sacrilegious and against the traditional customs of the Church. We can attend for a wedding, but only sit in the back and not participate.
Now, it is very crucial that parents agree in matters of religion, otherwise this will tear the family apart. I have known quite a number of families who split up because one parent was traditional Catholic and the kids to go with them to Mass, but the other parent was novus ordo and wanted the kids to go with them. So, it is definitely not advisable...
It is also important to remember that feelings change over time. So, it is wise to chose a spouse who will appreciate and your opinions, rather than just one who feels drawn towards you. It is not always easy, but in the long run you will be glad that you did so...