Apply for parents' immigration

If you and your father both have green cards:

You can't apply for immigration for your mother (you must be more than 2 1 American citizens to apply for immigration for your mother). But once you are 2 1 and become a citizen, you don't need to schedule your mother's green card.

Your father can help your mother with immigration (if they get married), but China people have to wait 4-5 years to get their spouses a green card for immigration. However, if your father becomes a citizen during the planning period, he can apply to upgrade the case to citizen spouse immigration without planning.

You can work out which method is faster.

One more thing, if your father immigrates for your mother now, your mother will not be able to get a visit visa to visit you within the schedule (if she is in China) because of her immigration tendency.