Welcome to the forum.
Healthy budget of £35k. Obviously factor in real cost of ownership. If you’re starting from scratch, then life-jackets, insurance, LED flare, PLB, VHF radio licence (unless you did that with military), offshore suits, anchor, ropes, etc. It all adds up.
I’ll dispel myth on Zodiac from my point of view. Leisure wise, great boats. These RIBs are fine for warmer climbs where sea conditions are a bit more predictable. Some of the smaller leisure boats have shallow V hulls and slap in short chop when the wind gets up. Most will be PVC slide on tubes. Some of the current open pros for example use Neoprene tubes. Everything with Zodiac, especially accessories is daft money. That said, it’s been a while since I bought anything boat related, so can only imagine it’s similar for most manufacturers.
Remember you don’t need to buy new. Work out exactly what you want. If you’ve used RIBs before then you’ll be used to something more utilitarian, but it comes down to seating (especially with a growing family), sea capability (so you get full use out of it) and power set-up, such as well maintained modern engine and more paperwork than a Brexit export.
Engine wise, most will be 4-stroke fuel injected. Go for maximum hp rated for the hull. Also work out if you want an auxiliary engine. North of the wall so-to-speak you can find yourself at sea with no-one close if you have a mechanical issue.
At home, then if under cover, also look at security devices, hitch lock, engine lock, wheel lock, tracker, etc. Unfortunately there’s a market for engines once stolen.
Ribeye A600 would be worth a look at, Delta 5.5m, indeed Ribcraft 585 has loyal following on here.