When do u let ur in law know u are pregnant ?

We havent told in law about pregnancy, cos we wish to wait after 3 mths. However, we will have family dinner at Dianxiaoer next week. Can I eat the herbal roasted duck? If I dont eat, they must be suspecting. I think we have to tell them soon. We went to JB today, and my mil wanted to have bak kut teh. My hubby told his mum that doctor said I cannot take herbal due to stomach flu. Hahha I almost laughed.