One thing's for sure - even if your elderly parents walked on water and are amazing people, taking care of yourself, your own kids, AND your aging parents is really hard.
On top of that, if you live in a state which has 'filial responsibility' laws on the books, the state could force you to have them move in with you and you'd have to take care of them anyway.
We do not live in one of those states, but just imagine how stressful one's situation could be if you live in a filial responsibility state and had a very toxic parent who's aging.
ODD (who's 18 and just started college) told me a few days before we dropped her off at college, "If Daddy dies first, then I'll just have you move in with me and my husband and our kids." I told her to hold off on making such plans...let's see how it all plays out and work on your own relationship with your spouse first.
With my MIL, we financially supported her for the last 16 years of her life. We went above and beyond what most people would have done. Even sacrificed putting savings into our kids' college funds for 16 years in order to help out my narcissistic MIL. It was really really really hard, especially when after all we'd given her over the years, she still acted like we didn't do enough. Years of having to keep info from her like us going on a short trip somewhere without her (she expected to be included on every family vacation and for us to pay for her; also expected that every time we went out to eat with her, that WE would pay, not her). I have zero regrets with her not living in our home with us. My own DH, her SON, couldn't handle having her live with us.

The ONE time we took her with us to
Disneyland? She didn't even offer to buy my kids an ice cream cone, but made sure to complain on the drive home about how she didn't get enough time to shop for herself and her friends.
Up until just a few weeks before she died, she refused to ever tell us anything about her multitude of health problems. Flat out refused to set up estate paperwork. Medical power of attorney? Nope, refused. years ago, had retina surgery and told the eye doctor that there was nobody available to drive her home, even though we were about 20 min drive from that physician. Checked herself into the ER once and didn't tell my husband until 2 days later when she needed a ride home from the hospital. I could go on and on about the stupid games she'd play.
I wish that everything was sunshine and rainbows for everybody in the 'sandwich generation' situations. But it's not always sunshine and rainbows. If you & your aging parents/parents-in-law can be understanding, caring, and up front with each other and work out a good system for everyone, then that's a wonderful thing!
But please don't judge others if they don't have such an arrangement. You don't know what kind of nonsense they've had to deal with over the years.