"To adopt the brothers" means to become their legal guardian and take responsibility for their care and well-being, as if they were your own family. Full definition
He found that having biological older brothers, not adopted brothers, was significantly linked to sexual orientation, regardless of whether a gay man was raised with them or not. (discovermagazine.com)
He hasn't been with any other cats except for his recently adopted brother, but if he is introduced slowly and properly he may get along with other cats just fine. (consciouscat.net)
The trailer also introduces two new characters — Tessa Thompson's Valkyrie and Jeff Goldblum's Grandmaster, one of the Elders of the Universe — as well as the return of Thor's meddlesome and apparently indestructible adopted brother Loki, played again by Tom Hiddleston. (rollingstone.com)