Aw, Obi! Sounds like he might have needed some comfort, too. Or felt your FIL did.
How much do the other animals miss the one who's gone? That's a whole 'nuther subject!
I lost my dearest little (enter endless string of love-words) greyhound last September, and was just devastated; crying all the time, angry, sad, shocked, lost, depressed ... I sewed her fuzziest coat into a pillow so I could still hold "her". Every morning I woke to the pain, like a lost limb; how could I go forward in THIS world, the one without Wabi?
Our two other greyhound boys, do not get along with each other all that well, though they both did with Wabi, but did they miss her? Would I even have noticed through my own pain? I don't think they really made much of her not being there. They didn't seem to look for her, or anticipate her return, like they do when one of us humans is away. *shrugging* Without Wabi around to lighten the mix, our family was more of a job - keeping the boys safe and as happy as possible - than a joy.
I was asked to foster a young, scared borzoi, rescued from a shelter in Korea, 3 months later. Though it was our firm intent to move Katie through to a good home, her light-hearted determination to find good things in this new scary world won us over pretty quickly. She did not replace Wabi, but there was a role that Wabi played in our home that Katie slipped into with bouncy grace. Our family works better with her in it. Obviously, we failed fostering, and Katie's still here.
I tell that story only to say, who knows how or why we join up with each new animal? We think we can explain some of what we do or think, but it mostly works on a lot deeper levels. Maybe you will get a kitten, even though you tell yourself that's somehow wrong. Trust your innards when the time comes. {{Hugs}}