what should i do?

hi. first post on here , hopefully i get some help on here. so my mom overheard a weird call between my dad and a male coworker that went something along the lines of : coworker: you and ***** (female coworker) didnt show up to work, i thought you finally decided to get her out of working and maintain her dad: cough and switches subject then she realized that my dad hasnt put his checks into their shared bank account. for months. and he doesnt wanna spend any money on us anymore. she also found a receipt sending a lot of money to mexico. maybe thats unrelated to whats going on but it's still suspicious. my mom wants to show up at his work and see whats happening but they wont let her in without a code. theres other suspicious stuff going on like him always accusing her of cheating, making her delete fb and so on. what do i do? how can i help find out the truth? what should we do about the bank stuff? that account pays everything, and it's really all just my moms money. oh also, just remembered, money has gone missing from some envelopes he keeps, yet he seemingly doesnt spend it, atleast not that we know of. any help? how do i catch him, if hes doing something?