I don't want them all just hanging around my heels all day
Your posts don't mention engaging with your dc, only how to get them to play by themselves.
Its all very well expecting the younger dc to entertain themselves for 30 mins or so here and there, and nothing wrong if that's sometimes TV but not all day, if they are sitting in front of screens all day its because they are bored stiff and not stimulated enough. The younger ones cant go and play with friends so you need to engage with them for most of the day whether it is going out to the local park or even shopping, walking the dog, helping with made up chores/gardening, helping you load the washing machine, encouraging play (set them up with paint, lego, and play with them) etc. Anything that stimulates their senses, takes them places where they learn how to behave, works on their major and minor gross motor skills more than sitting watching tv.
when ds was that age our weekend days would be something like breakfast, park for a couple of hours/or grandparents to play with, home for lunch, painting/help clear up, dinner, reading or a jigsaw/simple board games together, bed. Week days he was at nursery so it was really just dinner, bath time with toys, story and bed.
thankfully tablets/smartphones weren't really around until ds was about 10 and he'd already learned to play without them. We did have a Wii when he was around 6 or 7 but that was mainly Wii sports etc we played together.
Can the 9 year old get out and play with friends?