My cat had kittens. We kept a female and gave a male one away. The new home didn't work out so we took the male one back. Will they remember each other? They were separated for about a week and a half.
Absolutely, unless the kittens were newborn at the separation time.
Something amusing that I recall: I had a female cat that I took to my grandma's one summer. My grandma had a male cat at that time living in the house. Both cats got along quite well, but then I took my cat back to my home. When I brought her over to my grandma's again more than a year later, I expected some adjustment between the two to occur. To my surprise, they recognized each other immediately, like they had never got separated...