Hello Alfred,
I've been teaching here for 5 years, and I agree with what William King has said. The letter from the Ministry of Education is needed and can be difficult for schools to obtain depending on individual circumstances.
For example, when I first started teaching here, the minimum age for teachers at an international school was 28 and I was 25, so my school had some difficulty in getting approval from the Ministry of Education.
Assuming you meet all of the requirements of the Ministry of Education (age, years of experience, qualifications, etc.) 2 months does not seem to be too long to wait for the KITAS, especially considering the recent holidays.
I understand completely, however, the stress of feeling as though things are simply 'up in the air,' and in my experience, HR is usually reluctant to give you any information beyond, "Still in process." However, I would wait another week and then politely ask your HR where they are in the process exactly and if there are any issues. You may have to press a bit, but they might be able to give you some more concrete information.
They can't force you to teach, of course, but depending on your contract, you may be terminated and liable for any fees they may have already paid for the KITAS. This depends completely on the contract you signed. All the contracts I have had stipulated that the contract is void if there is no KITAS. (Which makes sense, you can't be their employee if you are not legally employed). However, if you decide not to go in and teach, it may make things rather difficult. Do you plan to stay in Indonesia?
It is the norm here to teach at a school while the KITAS is still processing. I hope that you get answers soon. I wouldn't be overstressed about it at this point, however.