In my case, I am the only one who do the teaching in my family. I used to speak Thai to him 100%, even when I did LR-English with him. He was really confused. When he started reading, he would read the English words in Thai, e.g when he saw "dog", he would read " ma".
I realized that did not work for us. I opt not to speak Thai when I do English lessons with him. Now, the only time I will speak English is when we watch LR/LM or other English lessons. This has worked for us. My son does not get confused anymore. He can comfortably switch langguages when he speaks to me and my husband (who only speaks English to him.)
I want to know what others have done too, so let's hear what other parents have to say about this.