Falsely accused of sexual assault

my dad is fully blind and has been a neuromuscular therapist for over 8ish years now. yesterday i got a letter in the mail from a lawyer stating that over a month ago my dad sexually assaulted one of his female clients. they are now requesting 1.1 million dollars for settlement by 3/9/26. i fully read through the letter and a lot of pieces don’t line up especially given that there is no evidence. among a list of 5-6 charges there’s sexual assault, assault, false imprisonment… it also stated that the massage room was unusually dark (it’s very common for massage places to have dim lights and for them to request the client to uncloth)my dad has actually been sexually abused by one of his own clients a few years ago but was too afraid to ever speak up. this isn’t something my dad would ever do and i feel like this is a set up. our family doesn’t have anywhere near 1.1 million to reach settlement so I’m wondering what happens when this case is taken to court? do i need to start looking into defense attorneys? how common are cases like this and do you guys have any advice or recommendations for defense attorneys or next steps?