Parents Visa Questions

My friend told me that parents who extended their visa before cannot get the visa again in Shanghai now. Is that true? Can anybody share some parents visa information?

My parents came to the US in Oct. 2001. My father stayed with us for 2 months. My mom extended her visa, she stayed for 11 months. It has been more than one year since she left USA last time. I'm thinking of inviting them to visit us again now. They will apply the visa in Beijing. Should I let them apply the visa separtely or together?

Thanks very much for all your attention.