I think there are more than a few of us who care from a distance - and it brings its' own guilt & worry just the same as if you were next door. I do hope that you can get some assistance for your in laws. In my case, it was identified probably 3 years ago that my mum needed some help and I was lucky to get 3 visits a day and then put in a private carer just for around an hour a day every 2nd day which was excellent; the private carer really organised my mother, sorted correspondence, made doctors appointments, made sure there was food in the house etc whereas the council carers, although excellent, just did the washing & dressing & making sure Mum had something to eat. Luckily Mum was quite amenable to having people come into her home which isn't always the case.
In retrospect, I think my mum realised that things were not good; she had recently (May time) started to ask all the time as to when we would visit next - we can only come up in the school holidays as my children are still young - and I can only think it was a cry for help.
The good thing is she seems very settled in the hospital; we are so lucky, she has her own room with a lovely view plus an en-suite. The only thing is that I feel a bit guilty as she technically does';t need to be in a hospital but things move so slowly and I am now finding my way regarding care homes & finances. And then I worry about the actual move to a care home and getting her settled in again as I know I will have to visit and facilitate that as well.
Does your partner have Power of Attorney? If not, would definitely recommend that someone in the family gets it set up as soon as possible. My mothers district nurse strongly suggested, 3 years ago, when my mum was first diagnosed with mild cognitive impairment, that I get it done. Me, in floods of tears thought I couldn't possibly - but I am so glad now that I did as it makes life much easier all round.
I am just focussing on the practicalities at the moment which gets me through. Hopefully your in laws have good neighbours - might be worthwhile alerting them to the situation, even if all they can do is to act as an early warning system.
There is so much good advice and support on this forum; I think all professionals dealing with elderly people should be made to read it! Wishing you strength and courage and do let us know how things go.