Separate litter tray from food are as much as possible as they don't like these being in close proximity. Put the litter tray somewhere as tucked away as possible as most cats need to feel quiet & safe before they will 'go'. Otherwise expect a present under the bed.
Block off all access under beds and furniture in the room that will be their 'safe space' and anywhere else you don't want them hiding or worse, getting wedged or stuck. There is nothing worse than trying to extricate a new frightened kitten that won't come out from behind the washing machine or in the furtherest dusty depths under a bed. Keep all wardrobe and kitchen cupboard doors shut as they are bound to go exploring and then someone shuts it and they go 'missing' for hours as you frantically call the name they haven't learnt yet.
Instead, give them various safe dark quiet spaces to hide that are easier for you to find them (a big cardboard box with a hole in it or the top flap down works well).
Make sure they have something to climb for a high up vantage point. Many cats feel safer up high and looking down on you (unless they are a dark space floor dweller, as above). A cat tree is best but anything hefty can be bodged to provide climbing options. If you don't it will use the curtains and perch on the rail, guaranteed.
Put away any dangling wires or cords, especially ones that if yanked hard enough could bring something heavy down on them. This includes all plugged in devices, router, TV's etc. Playful kittens will pounce on anything that looks fun!
Buy some cat toys and play with them regularly. Gets some of the manic energy out and helps bond with them. Get a scatching post or mat, cover your rugs or carpets, especially around doorways as they will scratch it to be let in if door shut.
Yes I have owned a fair few of the beasts.