I know this sounds cruel, but we don't owe our parents anything for just "bringing us up." Parents have to earn respect by, well, being good parents. My in laws were of the "we brought you up, but we won't pay for anything else after age 18 variety," screwing up my DH's life supremely. He was called stupid and told he was never going to be anything. Then, when he finished college and became successful, they were jealous and said that I made him a snob .
His other siblings kissed their butts as they spent every penny they had and expected to still live a nice lifestyle. We were seen as mean for not enabling them, and in the end they died destitute, my m-i-l spending the last 2 years of her life in a very nice assisted living facility, paid for by the taxpayers of Arizona.
My parents had no money in the end, either. My dad is 86, lives with "roommates" in their 60s and up until recently, worked 15-20 hours a week. He lives on social security, supplemented by a small check sent by me and more from my brother. But, the difference is, he doesn't expect anything from us. He is unrealistic, but makes it clear he still is "the parent." My brother has had to deal with his medical stuff, but it's kind of nothing compared to you guys. He is still active and his mind is fine. He reads more books than me. Realistically, he could live another 5-10 years, given his family history.
All I know is that I won't ruin my life because of his poor planning.