Daniele Venturelli/WireImage Maggie and Jake Gyllenhaal at the Venice premiere of her new film The Lost Daughter
The Academy Award nominee, 40, raved about his nieces Ramona, 14, and Gloria Ray, 9, who are "truly, and I'm not just saying this because it's an interview, two of the most incredible people," he told The Sunday Times.
"They come from a long line of incredible women and they're even more incredible than the ones before them," Jake added, referring to Maggie, 43, and their writer/director mother Naomi Foner, 75.
Jake said that he spent most of his nieces' childhoods only seeing them "at a dinner or a thing" and admitted that they don't watch his movies — but he's since had more time to bond with them. Recently, he said, the girls have been "coming to stay with me, you know, when my sister and my brother-in-law need a break, and actually having the time to say let's spend five days together."
He added that he's enjoyed getting "to know them and watching them grow up and actually sitting and listening to their experiences and the things that they're going through."
"Because they are the farthest from being a handful that you could imagine," he said. "And they're really not on their phones. Their father taught them a lot about the outdoors and the country, it's very important to him. So they find trees more interesting than phones, which is a rarity."
Maggie shares her daughters with actor husband Peter Sarsgaard, 50, whom she married in May 2009 in Italy, after they began dating in 2002.
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Jake previously praised his nieces during an interview with PEOPLE, in which he also said he's contemplated becoming a dad. "I want to continue becoming more of an adult than I already am. Hopefully with a family of my own," he said in 2017.
"My sister has raised two beautiful daughters. They are the most amazing girls," Jake added. "It's fun to send them home with a lot of candy, because it was almost like, 'Enjoy it, Mags!' A little payback for being the sister who made me perform weird shows at our parents' dinner parties."
The Velvet Buzzsaw actor supported Maggie earlier this month at the 78th Venice International Film Festival, walking the red carpet with his sister for the premiere of The Lost Daughter, her feature directorial debut. Sarsgaard was also there to support his wife.