I've been sketching all the important walrus characters from Wynstan the Wondrous. (From left to right: Wynstan, Wally, Chou-Chou, Aurora, Grace, Nerisse)
Missing from the picture is the walrus animus Aruk, who has decided that walruses are "falling behind" across the many worlds and the way to raise their impact is to mould them more into the profile of the most successful (in his opinion) inhabitants - like humans. Thus, on the world most similar to our earth, walruses in the wild and in captivity have been very rapidly "evolving". Some changes happen during a single lifetime! The closer the walruses are to humans (or another species similar to humans in various sorts of intelligence and communication), the faster this magic evolution happens.
Aurora and Grace were living in an aquarium, after being stranded as infants. They are genetically unrelated, but think of themselves as sisters. The changes hit them as they grew to adulthood, and when Wynstan and Wally were stranded as infants themselves many years later, they had mastered language to the point that they could communicate their desire to help raise the children (which they did).
Wynstan and Wally had already decided they were blood brothers while they were in the ICU, and therefore they developed a confusing brother/cousin situation when Aurora adopted Wally, and Grace adopted Wynstan.
They still live together in the aquarium, in private housing. Wally and Wynstan travel each day to a school for walruses, until Wynstan is offered board and tuition at The Place Of Learning at age 14, where he meets Chou-Chou. (Don't worry about Wally, he goes to sports college.)
Chou-Chou (and her mother Nerisse) grew up on a world where a newly expanded walrus society was deliberately invited into the world from outside, as part of a peculiar sideways play in the 4D-chess-cold-war between two entirely different complex civilisations. One of them was for the most part oceanic and aquatic, and the other was amphibious in shallower water, mostly on or around land. Between these two, the walruses cautiously made their home.
(this is all subject to change. I make no promises!)