It's normal, yes.
Two of our family cats, Skunk and Smoky grew up together, even though they were about a year apart in age. Once they became friends, they were inseparable. They're outdoor cats, per my dad's rules (one of the few he made, with my mother being the main rulemaker in the household). When they were about 9 and 10, Smoky died. She got hold of a poisoned gopher or something, I can't honestly remember right now. Skunk knew her best friend was gone. She stopped eating, grooming herself. You name it. I insisted we get another cat ASAP. My mother got a kitten, who couldn't go outside just yet, he'd have gotten his behind whupped by neighborhood toms. But I think Skunky knew there was a new boy in the household. As he got bigger, we invited Skunky inside to meet her new baby bro. It had been so long since we had a kitten, she wasn't so sure of him. The funniest moment (to me, at least) was the first time he went outside. he wanted to play, so he snuck up on Skunky as she walked along our sidewalk. he pounced on her tail and she turned and gave him a swift PAW to the head. He learned very quickly who was Queen o' the Yard. She is now about 17, and although she's not in perfect health, she's still Queen.
Your others will mend their broken hearts in time. They grieve for lost friends and siblings just as we do. Extra hugs and pettins' for them will help both you and them in this time.