Yes, we went one further and actually had four generations living under one roof at one point! It has some advantages caring for both older and younger generations as initially most older people can be trusted with modest after-school childcare responsibilities which helps to keep them actve and feeling valued, and it is also possible to recruit domestic care workers who can look after both simulataneously whilst you go out to work or do "me" things. The main downside is being willing to accept the ultimate possible need for a nursing or care home: you need to plan this from day one and involve the parent in making a choice whilst they are stillcapable. Also ensure they have signed a Power of Attorney and made a will whilst still capable so you can gradually take over financial and other decisions as events progress. You have done that, havent you?
"This is one of the hardest lessons for humans to learn. We cannot admit that things might be neither good nor evil, neither cruel nor kind, but simply callous - indifferent to all suffering, lacking all purpose." - Richard Dawkins