Re missing them - I made myself a rule and kept to it which was to never ever tell dd I missed her. I remember my mum saying that to me and it just broke me when I was feeling homesick. There's loads you can say instead - we're looking forward to seeing you, it's nice to hear from you, you look great, show me the room/flat/campus in FaceTime. If you go down the miss you line you will both end up in tears feeling crap!
Make plans for the weekends. The week isn't too bad but the weekends suck even if they spent most of it in their room. And watch out for the supermarket, it's surprisingly painful not needing to buy them the stuff they like. That does ease though, you just have to adjust.
That said I'm so glad dd2 is staying at home. She's joined a CU group chat and made contact with somebody on her course who knows her boyfriends parents, looking at freshers events etc. Still quite a long time before York get started!