My father-in-law was not abused, but he was not the favorite of his mother; that was his brother. His father worked a lot. His father died fairly young, and when his mother was elderly and dying of lung cancer, he took her in.
My father-in-law also is bipolar, knows it, and doesn’t take meds because he loves his manic highs too much. When on a high he acts like king of the world, and woe betide anyone who doesn’t wholeheartedly and sincerely (at least, a very good acting job of seeming sincere) agree with his opinions during those times, or else he turns into a screaming asshole who might yell for hours. He physically, mentally, and emotionally abused his children and wife, and I’ve heard worse rumors about things he may have done to his wife decades ago. He didn’t stop hitting the kids until they were at least teens or older; my husband stopped being beaten when he was in his late teens and caught his dad’s punch. That brought fear into his dad’s eyes, but didn’t cut down the yelling.
He also values people based on what they can do for him. If they don’t come through in a fashion that he expects, then he can go on about perceived slights for years to come. For just one example, a friend that he’s known for a few decades has been on his shitlist since November just because he wasn’t quite as good of a host as my FIL thought he should have been - the house wasn’t spotless when they visited, he and his other friends at the party ate/drank too much of what my FIL brought along, etc. Even learning that the friend was in extreme pain at the time due to a then-undiagnosed digestive ailment and so was unable to clean around the house as much as he would have liked did nothing to cool his anger.
(On his lows he’s just a little maudlin, but not really repentant or anything sympathetic.)
He didn’t allow his wife to work, and used the money that he got from his work on things that made him happy. Cars, other property like vacation cabins, expensive clothes for him, or just saving it up. My MIL was given a tiny allowance to run the house on and clothe herself and the kids. His wife and kids each had one nice outfit to keep up appearances, and their other clothing was found at thrift shops. The girls got jobs at clothing stores as soon as they could legally work, so they wouldn’t look so poverty-stricken at school.
I’ve said half-seriously that at least one of my sisters-in-law has “Stockholm Syndrome” about him. She goes to therapy still (and she’s in her 40s) to deal with the effects of his abuse, but whenever there’s a disagreement between her parents she automatically takes her father’s side and runs down her (very passive, maybe once passive-aggressive, but now suffering from dementia) mother.
My husband helps out his dad when his dad is ill, but has said he’d consider cutting him more or less out of his life, if it wasn’t for his mother. As for taking him in - my husband says he won’t get a place with more than one bedroom. He’ll give his dad care, but not really loving care, and his dad can use that hoarded money to pay for a nice senior care residence or nursing home.