You're insane if you skip a class date for two holiday days off.

If you really want to be an airline pilot, and intend on spending more than a year in this job, you need to get your priorities straight and train your family to never expect you to be home on a holiday (or any specific day for that matter). It's better to be upfront about things ilke this, and to set a realistic level of expectation with your loved ones before you even start groundschool--it'll save your marriage, relationships, and mental health if you just clear that up for yourself and your family NOW.

20 numbers of seniority can (and often does) mean:

1) Having a job vs. being furloughed for 8 years
2) Being stuck as a CA for 8 years vs. being stuck as an FO for 8 years
3) Holding a line for 8 years vs. being on reserve for 8 years
4) Commuting for 8 years vs. being based where you live for 8 years
5) Having the experience to get hired at a legacy 8+ years earlier than the guy a class behind you who missed upgrade/got furloughed
6) Having more money and better QOL over the next three decades of your life because of all of the above and more.

If I had been ONE class earlier when I was hired at Mesa, I would've been a CA 3-6 months earlier, and I would've been a lineholder roughly a year earlier--that's a lot of coin to give up just for a couple of days at home, and you'll probably be too anxious about groundschool to relax and enjoy your holidays off anyways.

Long story short--SENIORITY IS EVERYTHING. Buck up and take the earlier class date--there's a chance you'll still get one or both of those holidays off (check airmen/instructors aren't known for liking to work on holidays). And anyone in your life who can't handle you missing the holidays is going to be a problem in your pursuit of this profession in the future anyways--get it out now don't put a bandaid on it.