We highly recommend catifying your house to make the best use of the space and to fulfil your cats' natural behaviours of climbing, scratching, leaping and having various choices of places to nap
For outdoor access look into fence toppers, there are various companies that make different types of cat-proof fence toppers so research a few and see which is most cost-effective. We also love catios! If you can't get fence toppers then see if you can create a safe outdoor enclosure ('catio') for your cats that links to a window or cat flap on your house. Harness walking can be a good option too for some cats, but it very much depends on each individual cat. We recommend trying it starting from your back door rather than driving somewhere and getting out for a walk somewhere unknown.