Can China's overseas passport go directly to the United States from overseas?

No, as "Waipiao" said, there is no difference between China passport and overseas passport, but the location is different. The China government may know that your relatives have applied for China passports abroad.

In the past, the practice was like this: for example, a person working in a foreign company belongs to an employee sent by a foreign company to an overseas office and has a dual identity. Because the state stipulates that overseas offices are not independent legal persons and have no right to employ China citizens, it is said that companies such as FESCO and CIIC recruit first and then send them to overseas representative offices. Such a person, if sent abroad by a foreign businessman, should be private. Anyway, your boss sent you abroad instead of the State Council. There are a group of people who don't know each other, so they don't come back after going out and live abroad. When their passports expire, overseas embassies will not extend them and ask them to go back to China for processing. That is, the so-called passport is private, but because of the nature of public management.

But if he changes his passport through some channels, he can apply for an extension without restriction, which is the so-called overseas passport. But that was many years ago. I wonder if they are still like this?

As for traveling to the United States, your relatives are facing visa officials of the United States government. They only care about the relevant provisions of the immigration law for their citizens to apply for visas, regardless of where the applicant's passport is obtained.

As you are still a citizen of China, you must go back to the consulate where your original account is located (that is, your place of residence) to apply. If the registered permanent residence is different from the permanent address (such as working abroad), you need to provide relevant certificates and apply at the consulate of the permanent address, but you must apply at home.

According to what you said, he must apply to the Guangzhou Consulate.

In addition, I suggest that you don't consider going abroad in the name of working or studying abroad. China citizens' application in the United States is very strict, even if they have colored eyes, they usually go back to their places of registration. Even if you insist, you can apply, and it only costs a lot of money to get a statement of 2 14(B). If he has permanent residency or citizenship in Thailand, he can apply in Thailand. Refer to the first and third answers.