Breaking into a Mac?

Dear brain trust,

My father had a laptop, an old MacBook. My mother would like to know what's on it. It's password-protected. I've been unable to guess the password, even knowing some of his other passwords and some patterns he used.

I have the passwords to his two desktop computers (iMacs), but also can't get in via network share (access denied). I have his cell phone, which should let me get into his iCloud account (that's the second factor). I have the impression that none of that will help.

Is there any way I can override the laptop's password and get in anyway? Or connect an external drive and make a copy somehow? I'm willing to take the laptop and a copy of the death certificate to an Apple store, except that I don't know if it's technically possible to get in (without damaging the contents, which is the whole point of the operation). I mean, we'd all like security to actually be secure, so this shouldn't be easy, but is there something between "easy" and "impossible" that I can try?

The laptop is at my mom's house, so I can't test things immediately, but I'm looking for any clues that could help on my next visit.