Family reunion visa for Spain? (Valencia)

Hello,I am new here. I am Chinese and my husband is British. My son is British too. We live in China for years and we are moving to Spain.

I am supposed to get some kind of family reunion visa for Spain. But the problem is whether my husband has to go first, then I can apply in China or can I apply now and we will go together?

He does not have any Spanish resident certificate because he works in China for 11 years. If he has to go to resident in Spain first, it means we will have to separate for a few months. My boy is only 4 years old. It is really not nice for him to stay in Europe with dad or stay in China with me when I wait for the visa.

Can anybody give me some suggestion or help？

Thanks

Sandra