purchasing a macbook pro and trading in 3 devices towards purchase price

I am wondering how to order a macbook pro online and get the trade-in amount for 3 devices (older macbookpro, iphone 7 plus, ipad) to go towards this one purchase of a new macbook pro. I am also an educator so would like to know how to get that discount at purchase and the airpods. I did already use the website to evaluate the trade-in values and the message for each device said they were sending me the box to mail it back for the gift card. My concern is getting the device in time for the new school year. I'd like to make the purchase now and not have to wait to receive 3 giftcards. . . advice? Thank you.