flying to china in July, we have israeli passports and swiss permit c, living in canton Vaud.

Hello we are a mother and two daughters (aged 14 , 20) , we have been invited to volunteer in the Giant panda reserve in Chengdu , we already have our invitation letters, flights and accommodation. When can we apply for our visas? Do we all need to come to the embassy or can I , the mother, come with my daughters documents? Thank you.