Cat experts wanted!

I've run into a couple of cat issues with our pair of Rescue cats, one psychological and one more "digestive".

We are pretty sucessful generally with cat's and I like to think of myself as a "cat whisperer", but there comes a point where you need a bit of guidance.

1. My ginger boy alternates between eating healthily and just not being able to hold anything down. We've tried hairball remedy, all sorts of foods, but it just seems random. You can get quite a while out of him, but just when you thinking this combo works, it comes back..It seems to be connected to his vocal abiltiy. 

2. These are INDOOR CATS, we got 'em at ten years of age, I was told they were indoor only by cat's protection and that it would be nice to give them a run or even fence off the garden...

Well, we waited for 6 months, until they'd got some sort of a functioning relationship with us, before (whilst i was down south visiting a mate) my O/H unilaterally decided to give the orange boy some garden time, which he was obviously quite keen to have... By the time I got home a week later this was a regular gig. 

Well it was bloody great at first! They ate grass, (both are really, really keen on a bit of fresh grass), orange boy used the facilities outdoors, (vastly reducing my workload!) and they both really, really liked it for about a month. Then they started wanting more & more... 4 "escapes" later, (which ever one it is always come back real quick) and I'm at my wits end. They are REALLY resourceful!! I simply cannot convert them into "outdoor cats" at ten years of age, (even if the cats protection people would forgive me) but they seem so damn determined to explore. 

Our belief is that they didn't get the same level of "interest and interaction" from their previous human staff, and they seem to be coming along really well, especially the one who only reliably responds to the full appellation "Queen Missy Spud the first". Unfortunately, as my 01:15 experience up on the garage roof attempting to rescue the golden boy, followed by my 01:30 foray into the next door neighbours (very secure) garden via ladder with cat basket in hand, indicates, we don't yet quite have the level of understanding and trust that I usually get to enjoy. But it has only been six months... Gaining that proper trust and understanding with a cat can be a multiyear project I know. (getting past that point where they stop "masking", and treat you more like a companion and less like a "keeper".

We lack the resources to get an eight foot high fence around the garden, a "professional company" quoted us £2,000 just for bits of plastic and wire supports, with a plan that would not have worked anyway on our bottom fence, so whilst I keep plugging the gaps as they find them*, any hints as to ways to reduce their wanderlust would be greatly appreciated! (I never thought he'd even consider, much less easily execute a 7 foot drop from an upper story window onto a shed roof, although I never leave that particular window more than a crack open anyway...)