Thank you Mr Tomkiel for the answers. You did not answer my second question about parents receiving a reduced social security benefit , probably because I phrased it incorrectly. I understand that 85% of their social security income is taxed because of the higher AGI. My question is about the reduced social security benefit they receive every month - the checks are less - apparently because their total income (AGI) last year exceeded some trigger.
Sorry about that! The higher income does NOT affect the SS benefits under Title II (the regular SS benefits based on someone's earnings record).
But income does affect SSI payments if they receive them. It's possible to receive both kinds, and both are paid by SSA, so its easy (and common) to confuse them.
SSI payments are based on need, so income and assets are considered. Because a house may be excluded from countable assets for SSI purposes, the proceeds from the sale may now disqualify them for such payments if that is what they have been getting.
Or they may have elected to have taxes withheld from their SS benefits.
Ordinarily, whenever there is a change in benefit payments SSA will send a letter to explain the change. The letter might come some time after the change.