Here's a good point of discussion.
Have you thought of asking them whether the people before the Novus Ordo mess that couldn't read could follow what was going on?
In other words, anyone that didn't understand Latin was going to Hell, or was a bad Catholic? No! Of course not. Only the educated could read and understand Latin, and the illiterate still were able to see the reverent beautiful actions of the priest in order to follow along with the Mass.
The Mass being in Latin does not seem to keep them away from the true Mass, but Liberalism does.
From Liberalism is a Sin:
"It follows, therefore, that Liberalism denies the absolute jurisdiction of Jesus Christ, who is God, over individuals and over society, and, by consequence, repudiates the jurisdiction which God has delegated to the visible head of the Church over each and all of the faithful, whatever their condition or rank in life. It moreover denies the necessity of divine revelation and obligation of every one to accept that revelation under pain of eternal perdition. It denies the formal motive for faith, viz., the authority of God revealing, and admits only as much of revealed doctrine as it chooses or comprehends within its own narrow capacity. It denies the infallible magistracy of the Church and of the Pope, and consequently all the doctrines defined and taught by this divine authority. In short it sets itself up as the measure and rule of faith, and so really shuts out revelation altogether. It denies everything which it itself does not proclaim. It negates everything which it itself does not affirm. But not being able to affirm any truth beyond its own reach, it denies the possibility of any truth which it does not comprehend. The revelation of truth above human reason it, therefore, debars at the outset. The divinity of Jesus Christ is beyond its horoscope. The Church is outside its comprehension. The submission of human reason to the Word of Christ or its divinely constituted exponent is to it intolerable. It is, therefore, the radical and universal denial of all divine truth and Christian dogma, the primal type of all heresy, and the supreme rebellion against the authority of God and His Church. With Lucifer its maxim is: "I will not serve." "
Liberals view the Catholic religion as intellectually sensible, and it's really a "bonus" that God revealed it. Therefore they believe it only because it makes sense to them, but not because God revealed it. That is why they're so comfortable saying that there is salvation outside the Church, because if they said there wasn't, they'd be including themselves since there is no real Faith there, but only an intellectual understanding.
Hopefully you can pray for an increase in Faith on the part of your parents, and ask them...
"Did the people that went to a Latin Mass 1000 years ago not understand what was going on? Most people back then couldn't read unless they were rich, and Our Lord said that rich men have a hard time getting to heaven because of attachment to the things of the world. Being attached to the (English language) is also being attached, because it's "easier" for you to understand it. It's not about what language the priest speaks in, or whether or not you can understand it. It's about what is going on up there, and what the priest is doing on YOUR behalf that means something. And until you get used to it, there is a missal you can follow along with that has (English) on one side, and Latin on the other."