filing of gst return

you should file gstr 3b for July and august

First you need to file GSTR -3B form. Then you will be in a position to file GSTR -1 form. You will have to check date of liability. If you got GST no in August but date of liability is effective from July you will have to file return for July & August. If it is from August then for the month of August only.
you need not charge GST @ 5% on every bill. As consignee is required to pay transport charge on RCM basis , you need not to pay on those bills. only of unregistered parties whose goods you booked, you to pay.

thanks for your reply