That's absolutely ridiculous, and quite selfish of your family I feel.
So he's got 35 hours between work, subtracting 8 hours sleep for both the 24th and 25th that leaves 19 hours, the drive for the way to your parents house and back takes up 12 hours, so then you'd both only have 7 hours to spend with them. And that time excludes everything else from traffic, eating, showering, general getting ready, and who the **** only sleeps for 8 hours around Christmas, 7 hours is the maximum time?
Oh wait does that even work out? So let's put an actual realistic timescale on this....
Boyfriend gets home on xmas eve at 10, sleeps from 11-6am (thinking of an 8hrs min.), you both leave at 7am after getting ready for the 6 hour drive, arriving at 1pm, then blah blah christmas stuff. But he's got to be at work for 7am, so working backwards, get up at 6am for getting ready and travelling to work, 8 hours sleep means he needs to be in bed by 10pm, 6 hour drive means you'd need to leave at 4pm. So you'd have 3 hours in between.
If any of those calculations are wrong, don't no one dare try to correct them cus that's not the most important thing here - 12 hours driving for 3 hours of forced christmas stuff is not a reasonable request of your family.
Here's some other things to put in perspective: But by your families reaction, christmas is important to them. If they have requested that you leave your boyfriend on his own for christmas, that is shocking. I generally don't agree with things like celebrating birthdays and christmas, they just seem stupid and pointless to me, but for a group of people who are already spending christmas together to suggest someone else should spend it alone, even I can see that is shocking.
You've acknowledged the problem early on by spending a week at home to try to make up for it, it's not like you've completely purposefully abandoned them. Like they're trying to get you to abandon your boyfriend? You're an adult couple, that live together and have been together for that long, that's a successful relationship.
To the person that said 'relationships come and go but family stays'. Well, exactly, family stays. If this is a successful relationship surely it makes more sense to keep a good thing going. What exactly are you trying to say by that, is she supposed to say- 'sorry boyfriend, but my family have summoned me, therefore I must go, just as you will be gone eventually'. Wow way to be optimistic.
I don't even know if any real point has been made there, I;m so bad at writing stuff like advice. But all I can think is if that were my situation and my family. I'd just present them with that reasoning of the timescale, remind them that texting, phone calls, Skype/facetime exist, it's not like you purposely want to avoid them, there are other ways of being together/staying in live contact. But after their reaction and saying that you're ruining Christmas for all of them, I'd straight up tell them that I'm disappointed in them for that level of selfishness and ignorance, but you know actually saying that I don't imagine would improve things at all. But deffo the timescale, and that they're being unreasonable about it