Bruce Jenner has long enjoyed a close relationship with his three stepdaughters from his 23-year marriage to reality-TV matriarch Kris.
But lately that relationship has been tested as the gap widens between the Jenner and Kardashian families.
In recent months, Jenner's transgender journey has made headlines around the world – and although they are supportive, his stepdaughters have also struggled with the news.
Kourtney, 35, Kim, 34, and Khloé, 30, "were the last ones let in on it all," a Kardashian insider tells PEOPLE in this week's cover story.
That's in contrast to Jenner's children from his previous marriages – Burt, 36, Cassandra, 34, Brandon, 33, and Brody, 31 – who had known about the possibility of their dad's transition "for years," says a source close to them.
As for the two daughters he shares with Kris – Kendall, 19, and Kylie, 17 – "they are having a hard time with the transition," adds the family insider. "They're very supportive, but it's just not an easy situation."
Reporting by JENNIFER GARCIA
For much more on how Bruce's family is handling his transgender journey, pick up this week's issue of PEOPLE, on newsstands Friday