This is something I struggle with massively, they say the RF are unsupportive (though they try an hide that behind meaning royal aides sometimes) but from the book:
The Queen was so supportive, praising Meghan, taking her with her on a trip quicker than any other royal and popping in to see them regularly at Windsor. She invited her to the big BP christmas lunch and the more private family Christmas at Sandirngham while they were still 'only' engaged which, I believe for HM , is a big step/sign.
Charles loves Meghan and her can do attitude and was like a second father to her. He and Camilla attended her private baptism and hosted a private dinner for Meghan after it with all her friends invited, he walked her down the aisle when her father couldn't and they spent some time at the Castle of Mey together. Charles was and still is continuing to still fund them and their lifestlye
Eugenie was wonderful, popping in all the time, double dates with H&M and Jack.
Zara is mentioned as being told about the birth of Archie via whatsapp
Even William is praised for fighting for them to have their own staff rather than just sharing with the rest of the RF and said to have pushed Charles to ensure their office was properly funded. At the start the book specifically says: But she needn’t have worried. As soon as William opened the black double doors to welcome Meghan into his home, he said, “I was looking forward to meeting the girl who has put that silly grin on my brother’s face.”
He and Kate host Meghan and Harry for Christmas in their own private home
At the start (before the book suddenly changes its view and Kate is cold and unkind) she is said to be supportive. Here is the entire quote about their first meeting which took place after William first met Meghan because Kate was still at Anmer at the time with the children (completely fair IMO surely and if anything shows how eager William was to meet Meghan not to wait until Kate was free):
Despite the fact that Harry was a regular guest in her household, Kate had seemingly not shown much interest in finding out who this woman was who had made her brother-in-law so happy. But that indifference wasn’t necessarily directed toward Meghan. “The Duchess is an extremely guarded person,” a friend explained. After she married William, she was careful about letting others in to her social circle. Her friends today—including Lady Laura Meade and Emilia Jardine-Paterson, both of whom married friends of William’s—are for the most part the same ones she had on her wedding day. Like her husband, Kate ran in a tight group.
Meghan brought a present for the duchess, who had celebrated her birthday just a day earlier. The soft leather Smythson notebook helped to break the ice, as did Meghan’s cooing over then twenty-month-old Charlotte. The meeting ended with Kate letting Meghan know that she was always welcome to contact her if she needed anything. Having been through the experience of being a royal girlfriend herself, Kate knew how trying it could be to suddenly have one’s personal life laid bare.
Kate may be cold, a bit distant but other than instantly becoming BFFs like some cheesy teen film I don't know what else she was expected to do. She told Meghan she could contact her with anything so IMO that in a way puts the ball back in Meghans court.
But all of this isn't supportive enough? Especially when you compare it to Meghan's family? I find that quite remarkable to be honest.