Thats not entirely true of Madelyne. When she was cloned, she was a blank, empty canvas. She awoke with fragmented memories of Jean's childhood (due to the Phoenix using a portion of Jean's soul to animate her) but those were more like random flashes than real memories and experinces. She definitely does not have Jean's memories up until the 90s. The opposite is true bc Jean absorbed Maddie's psyche in Inferno and left that arc with all of her memories. The same is not true of Maddie
In Dark Web, Jean did share her memories of raising Nathan but thats all. The life that Jean has lived are not apart of Maddie's mind.