The sisters are opening up about their past and being grandmothers.
The sisters sat down with ET to "Spill the E-Tea" and got emotional talking about their relationship, their kids, and being grandparents.
"What is the best part of having me as your big sister?" Kathy asks Kim.
"Oh, anything, so I get to say there are many parts to help me as a big sister that I love so much. One I just love, I look up to you for everything that you do. I look at it and I admire it," Kim says.
While getting emotional, she continues, "I love love. I look up to you ... You're like my biggest supporter. You're always behind me and always encouraging me and when I think I can't do something, I know you believe I can."
"I love that we laugh together. I love when we have fun together. And I love our relationship. I'm super grateful," Kim adds. "We do have fun together. We really do. And I think also the other thing is you're very patient with me and that's huge because sometimes I need that. You know I don't have a husband, I don't have Mom, I don't have my kids. And of course, I don't want to let them in on everything. So when I tell you something, you're patient and you guide me and tell me what you would do and I have to say most of the time I listened to you. There's a few things that I say here and there like, 'Oh that might not work for me,' but for the most part, the advice you give me I take and I love it and I'm grateful for it."
Kathy is the daughter of Kathleen and Larry Avanzino. Kathy's parents later divorced, and her mother married Kenneth E. Richards, who already had three grown children from a previous marriage, and had Hilton's two maternal half-sisters: actresses Kim and Kyle Richards.
"I have a question," Kim says. "You know, Mom [being] pregnant with me and coming home ... Do you remember the day I came home and how you felt?"
"I do. I was so excited," Kathy says. It was like having a little living doll and I was so proud. I was so excited because I've been the only child for five years. So I was thrilled to have -- you know, go into the nursery in the morning and just look at you and poke at you to try to wake you up so that I can pick you up."
The sisters also take the time to discuss being grandmothers.
"Who do you think spoils their grandchildren more, you or me?" Kathy asks.
"Oh, I think we're both guilty of it," Kim says.
"Nicky and Barron, and Paris. It's too early to see [Paris'] baby yet. But they don't want, like, all of this. Every day is Christmas. and they're right," Kathy adds.
"Any time I bring them something, they have to give something away," Kim says. "So they have to give something to children that don't have anything."
“Oh, that's good,” Kathy adds.
Kathy married Richard Hilton on Nov. 24, 1979 when she was 20 years old. They have four children: Paris, Nicky, Barron and Conrad. Kathy has six grandchildren, three by Nicky, two by Barron, and one by Paris.
In 1985, Kim married Monty Brinson, and they had one daughter together, Brooke. Monty and Kim divorced amicably in 1988 and later that year, she married Gregg Davis and they had two children together: a daughter, Whitney, and a son, Chad. Kim and Gregg divorced in 1991. Kim was in a relationship with aircraft-parts supplier John Jackson from 1992 to 1996 and gave birth to their daughter, Kimberly.
Kim has two grandsons through her oldest daughter, Brooke, and husband, Thayer Wiederhorn: Hucksley and Hunter.
During Kim's time on The Real Housewives of Beverly Hills, fans watched as the former reality star went through struggles, including admitting to substance abuse issues.
"It really is so beautiful to see you. Whitney and I were talking after the charity event the other day and she just said, 'I'm so grateful and happy. My mom, her energy is so pure. It's so good.' You have, you've had a struggle in life, everybody has a struggle," Kathy tells her sister.
"You know what they say right? They say those of us who have a little bit more than others or we've had our share and you've had your share too, Kathy, lots of big ones," Kim says. "And I feel like with everything that's happened to me that's difficult, or hard or hurtful, there's something that's waiting, a gift."
"What can I take from this? And what can I do differently? And that's something that I try to apply in every which way," Kim adds.
Fans of RHOBH will soon get to see more of Kim as she’s been spotted filming for the upcoming season.
"They've been asking for a while," Kim explained, sharing that Bravo exec Andy Cohen has been asking for her return for some time now. "Andy called, I think a year or two ago, and I said, 'Oh, not yet.'"
"And I think it was just that moment," she added, regarding the recently released photos of her hiking with some of the RHOBH ladies.
It's been something Kyle said she's been asking her sister to do, as well, but for Kim, her decision to film has been based on how she's feeling, and more importantly, the drama taking place on the show at that given moment.
"She's always saying, 'Tomorrow, cameras are up, just so you know,' and I make my decision based on how I'm feeling that day, and what I've got planned, and what drama's going on in the crowd," Kim shared. "And I just thought it was time."
Kim previously appeared on the long-running reality series in seasons 1 through 5 and has made several guest appearances over the years. Kathy, meanwhile, joined the cast last year.