SPT, our parents have made their own decisions. If they avoid consequences, or we can help them avoid consequences, all well and good. If chickens do come home to roost, we should not beat ourselves up, but instead simply do whatever we can to help.
Your father in law decided to live abroad. He decided to give POA to his neighbiour. He decided not to discuss his preferences with his family. All of these might have been decisions by default, but decisions none the less.
Assuming he has enjoyed his retirement in Spain, he might well make the same decisions again. Yes its tough now he is ill and you are so far away, but it would be tough in the UK as well. My mother is very comfortable in her sheltered housing and could plod on for years, slowing declining till she winds up bedridden in a foetal position. Living life, with only half an eye on consequences, may be wise after all.
I'm facing something similar. DM, who has always enjoyed amazing health, has a few symptoms which could be early signs of something more serious. The GP will run some more basic tests which might lead to a straightford and treatable diagnosis, or we face a decision about whether to put her forward for more invasive tests, which if it were something serious, could give the chance for early and effective, though probably not pleasant, treatment.
There are still a few bridges to cross, but the GP has flagged up that he probably wont recommend invasive testing. I don't have strong views, but see enough of my mother, and know how reduced she/her life already is, to want her to avoid the bed-ridden dementia end stage. (Her own mother was like this for three years.) The carer, who has formed a good bond and indeed picked up the fairly mild symptoms, believes all humans should have the right to treatment and the GP only wants to save money. My mother is failing to understand she may be ill, as she is not in pain, indeed pain seems to be her only concern. The priest has told me previously that my mother has had enough and indicated that I should not feel obliged to use all means to extend her life. My brother has suggested in the past that he wants my mother to have access to top quality private treatment when she needs it. However at that point he seemed to be in denial about how disabling her dementia was. I dont know if his views have changed or if he will share them with me. (I suspect it will be easier for him to have me to make a decision he would not want to make.)
If it proves to be something serious and life limiting, I will feel very guilty if I know she is ill because I opted for her not to have tests.
Its not necessarily easier if you do have control!