Is invitation still necessary in applying visa for firs timers?

I will be accompanying my sister and 2 nieces for a 4 day vacation to my brother's residence in Shanghai. It's already my 5th times entering China but first for my sister & nieces, is invitation still necessary to be submitted in applying the visa? we're leaving by end of this month, thus, i need to work on this as early as now. would appreciate your immediate reply. thanks.