Both my parents in-law get the maximum Spanish state pension which is 2,560 euros per month each. Plus they have private pensions on top

There is no minimum state pension in Spain. You only get a pension if you have worked at least x number of years (35 years I think). In which case then yes the minimum is 600 euros for a single person or 780 euros if the person is married

Although remember that there are 14 payments per year. Meaning that the state pension is between 8,400 and 36,000 euros per year

It's well known that pensioners are very well off in Spain. Often pensioners are supporting their children and grandchildren on their very generous pensions