@Marina810 this has to be really stressful for you and awful for your parents. @Branka-and-Silvia0 @Gordon0 have all given factual and real info about Airbnb and what you need to know. they are NOT vetting or checking people.
I am sorry if I move to a more emotional, real possibility - Airbnb is a booking agent and they can not and do not protect Hosts, Police can and do that job. So please know when we are unsafe we contact Police first!!!
This sounds very scarey to me - firstly, your folks can't communicate with this guest - we DO NOT know the persons agenda in being there for 1 month. That is a terribly long time to subject your parents to him.
I would suggest that all paperwork, their information, mail and anything personal, bank stuff or anything is locked away and not accessible to this person. If he is a criminal, he will not be following anybodies house rules, and so I think it is a very bad thing that he is there.
If it was my parents - I would NOT be able to tolerate this in their home for one month with a scammer, crook, criminal......Perhaps he is trying to also get info and steal their ID's. Since they can NOT communicate with this person. If this person doesn't give their Passport ID, which I would be surprised if he does. I would contact local police and have them intervene that your parents are very vulernable and since this is a criminal - They DO NOT have to continue hosting this person.
After police are involved Then call Airbnb....and they must take care of all communication with guests and rehousing or whatever they do with the guests. I would suggest after police - have your parents NOT there.
keep us posted. I hope your parents will be safe and sound and this will be over quickly.
blessings, Clara