中信免麵簽

I would like to invite my parents again. They stayed here for only 1 month
last August. And they are qualified for 中信免麵簽.

Since I am expecting a baby, this time I would like them to stay for 6 months.
But most of the 中信 cases are only for 3 months. I don't know what is the
chance that my parents will succeed if they ask for 6 months.

Should they only ask for 3 months, and hope to get 6 months when they arrive
here? If that is the case, what I should do to extend from 3 months to 6
months, then to 1 year?

Any suggestions? thanks,