The Middletons were definitely not accepted as PLU by the wider royal family and especially their courtiers in the first few years of K&W's marriage.
So many stories about how common Carol's roots were, how 'new money' her taste in decorations were, how much she'd influenced the decorations at Anmer Hall with her middle class ways, how she was getting above herself sweeping into the royal residences like she owned them, how the Middleton's were having too much influence and time with the grandkids and not letting Charles have his turn.
It interestingly culminated in a big DM article in August 2016 from 'sources close to Charles' that said the Middleton's were being edged out of attendence at royal events and were not being invited to stay with Charles at Birkhill for the annual Balmoral holiday, implying that the Middleton's had got a bit above themselves and were persona non grata.
Queue the late Queen doing what she did best - showing not telling - and we get less than a month later the 'pap' shots of the Queen driving Carol Middleton and also Kate all over the Balmoral estate - Carol in the front seat chatting away with the Queen, and news that the Middletons were not staying with Charles that year because they'd been invited to stay in the big house with the Queen.
And that's a big clear message to everyone media, courtiers, grumbling family members. The boss gives her stamp of approval - Middleton's are in to stay.
I'm sure they could have managed something similar for Meghan's Dad if she'd wanted them to.