SIL has my in-laws brainwashed 😢

So just a heads up, I’m going to be a little vague on some of the details to maintain some anonymity just in case.

We were at my in-laws over the holidays & the topic of helping their children financially came up. They expressed great sorrow & guilt that they hadn’t been able to help more. They always provide a safe home, with food & basic needs, plus some wants and helped with phone bills and car insurance while their kids were in school. But since they weren’t able to pay for college or a down payment on the 1st home, they felt like inadequate parents?!? My husband and I did all we could to reassure them that was unnecessary & all their help & love was all that was needed & greatly appreciated. But then something really surprising was said... that they had helped my husband’s sister “least of all”! So just a little context, my husband moved out at 18 & other than the previous mentioned car insurance & phone for 5 years while he was in school, no other financial assistance was given (nor was it desired). My SIL on the other hand lived at home until age 30+ working at most 10 hours a week (the majority of the time she had no job) & never contributing financially. She also in that time had 2 children who my in-laws provided for 100%, diapers, food, everything. They provided vehicles, gas, money to buy Christmas presents, everything she might need & want in that time. Both my husband & I’s jaws dropped when they said they had helped her least of all their children (they have others, all who have been independent adults with jobs since 18 or at lest since finishing college) we didn’t know what to even say other than reiterate how much we loved & appreciated them.

Another recent occasion I over heard my MIL lamenting to a friend how my SILs husband told them a medical procedure they allowed my SIL to have as a teen was the root cause of every problem she’s had in life (many problems my husband confirms she had before this was done & he says she begged & insisted on having even though my in laws had to put themselves in horrible debt to pay for it)

My MIL has also tearfully told us about how they never once went to her school/ sport events like they did for their other kids. Even though my husband has many specific memories of being there with his parents cheering her on.

It’s so sad and messed up the guilt trips she lays on them. If we do try to say something to the contrary we are scolded for “attacking” his sister. Idk what to say or do, but as they get older & in worse health it seems to weigh more & more on them the things she says.