Divorcee trying to visit son who is a Chinese citizen

so it was usually easy to get a residence permit, which I had until January this year. Because of an incident in my home country I had to stay longer in my home country. Now I wanna go back China and stay with my son, his mother have been divorced for 2 years and he lives with his grandparents. He is 6 years old so obviously he can't send me an invitation. My ex parents in law and I have a good relationship and it would be easy to get an invitation letter from them. I do wanna know how to get the q1 from germany. All the notarized documents are with my ex parents in law and it would be a hassle to send them over to Germany. Besides its too dangerous to send a birth certificate. What to do now?