Schengen visa question: We want our Thai son and his wife to come to the Netherlands for a holiday

I, a Dutch citizen by birth, and my wife (Thai by birth with a Dutch passport) want to bring our Thai son (my stepson) and his Thai wife to the Netherlands for a 2-week holiday. They are officially married. Both have a job with the same employer (pharmaceutical company) in Bangkok. They are allowed to leave the employer for a maximum of 2 weeks (in March/April), the employer can put this in writing.

There is a private home in Bangkok in the son's name. Have your own car with a repayment contract. Salary every month and a reasonably full bank account.
They will stay at our house (in the Netherlands). The son also visited the Netherlands twice more than 15 years ago, but we cannot find that old passport.

What is the easiest way to get a Schengen visa for both? Which request? Request for tourist or stay with family? Do one or more documents need to be officially translated from Thai to Dutch or English? We are trying to obtain an English statement from the employer.

Please provide advice regarding the method that has a good chance of success and which documents really need to be translated for that application.

Other tips are of course also welcome.

Thank you in advance.