Why am I getting duplicate photos on my camera roll?

I recently upgraded my phone from an iPhone 8 to an 11. Once I signed into my I cloud I thought everything was set. A day later I started getting duplicate photos and then being out of order. Also I’ve been getting old pictures that were on my stream (MAC) but not on my phone. So now, my computer is downloading them to my iCloud app..what’s going on? When this is done uploading all 7,000 of my pictures. If I delete them will they stop coming back?