The reason for all of this is repulsively simple as it proceeds from muttonhead Elly completely failing to understand what was going on around her. As we know, Marian genuinely needed help taking care of Phil because she and Jim had a shop to run. She didn't really want to have to talk Elly into giving up free time she deserved but since they were kind of tight for money what with wanting to fill up the coffers of two college funds, Elly had to take one for the team at age eight in order to have a better life later on. This led to problems for her grandchildren because like Jim, Marian made the horrible mistake of overestimating how smart Elly was. It seems obvious that Marian didn't think her daughter would see this unpleasant and anomalous necessity that Mommy was forced to do as being anything sort of a normal pattern.
While she never actually witnessed it when she did have contact with her grandchildren, she was way off base on that one because she and Jim never really understood that Elly was devoted to maintaining her lunatic misapprehensions as to what was expected of her. That meant that since they only had the briefest of contact with the kids growing up, Jim and Marian had no real idea that Elly and her husband distorted their comment about how it'd be nice if she were to help out without being asked into a series of demeaning lectures about ingratitude that had the end result of teaching her children that kids owe their parents the air they breathe.
Given Lynn's need not to admit that just maybe, Elly is a self-serving jerkass, something else will also be sure to occur. That certainty is that Françoise and Thérèse will be seen as wanting to selfishly and criminally defy all that is right and proper by suggesting that just maybe, Elly didn't quite understand what was going on around her growing up and mistook an exception for a rule. It's not that Elly and all of the other Pattersons are thin-skinned chowderheads that can't deal with kids at all well and are also kind of lazy, it's that Evil French People want to enslave them in their family politics.