A US K-4 visa will only be valid when your Thai spouse is holding a US K-3 visa. Once the Thai spouse receives a green card or a permanent resident visa, the children would not be eligible to receive the US K-4 visa.
For you to be sure that your family will be able to travel together, you should start the process for every person at the same time by filing a separate Form I-130 for everyone moving to the United States.
US K-4 Visa Application process in Thailand
Filing the I-130 Form
- The Form I-130 is a petition wherein an American citizen sponsors a foreigner for immigration purposes. The US national needs to file a Form I-130 with the USCIS to begin the application process for any of the K visas. Though only you are required to file an I-130 petition for your Thai spouse, United States Immigration recommends that you also file a separate I-130 for a K visa simultaneously. This would ensure that the whole family would be permitted to immigrate together.
Once your Thai spouse receives the US K-3 Visa instruction packet from the US Embassy in Bangkok, you should then start gathering all the required documents and fill out the necessary forms. The fastest method in completing a US K-4 visa application process is by gathering all US K-3 documents of your Thai spouse, and then the US K-4 documents for your stepchildren simultaneously. Separate forms are needed for each applicant, and it is important that you follow the instructions carefully. Everyone applying for the US K-4 visa needs to submit a birth certificate. You can also use school, baptismal or hospital records if there is no available birth certificate. A valid passport and two passport-sized photos are also needed from all the US K-4 visa applicants.
The Thai wife is required to show proof that she has permanent custody of any minor children applying for the US K-4 visa. This requirement can be met by producing a divorce decree with her granted permanent custody of the child, provided that the child is born from her previous marriage or an official statement from the Thai court or local Amphur granting your Thai spouse permanent custody and permission to move the child or children to the United States permanently. For child applicants 16 years or older, you will be required to obtain a certificate from the local police showing that the child has no criminal record.