What makes you think the family paid for it? Alaska is saying they did not. Again, they did not indicate that they needed assistance when they purchased the boarding pass.
This article below says the family requested it. I doubt very seriously that service comes free. If it does, I’d be shocked. The peanuts on flight don’t come free anymore.
https://www.kxly.com/news/spokane-family-sues-alaska-airlines-for-mothers-escalator-fall/678606175