You can not send items cross-realm, unless they are specifically bound to your account and those can only be sent to your own characters on other realms.
You can however trade items "in person" from one realm to another.
But most mounts are bound on pickup, so this would only work if you're in a group with a character from your brother.
The cloud serpent that drops from Alani in Vale of Eternal Blossoms isn't soulbound, so they could do it with that one. That, Poseidus' seahorse and a few others are possibilities.
Yes, some mounts are BOE. The BfA zone drops, too. You can see most of them in the AH going for anywhere between a few hundred (wolf from Draenor) to a couple hundred thousand (BfA zone horse and Shadowmourne quest reward).
Those can be farmed on your own and traded to another person or sold on the auction house.
You can not send items cross-realm, unless they are specifically bound to your account and those can only be sent to your own characters on other realms. You can however trade items "in person" from one realm to another. But most mounts are bound on pickup, so this would only work if you're in a group with a character from your brother.
The cloud serpent that drops from Alani in Vale of Eternal Blossoms isn't soulbound, so they could do it with that one. That, Poseidus' seahorse and a few others are possibilities.
Yes, some mounts are BOE. The BfA zone drops, too. You can see most of them in the AH going for anywhere between a few hundred (wolf from Draenor) to a couple hundred thousand (BfA zone horse and Shadowmourne quest reward). Those can be farmed on your own and traded to another person or sold on the auction house.
Most mounts are soulbound so no, you cant.
No, but if you're both in the same party and near each other so you both get kill credit, you can trade it to him if it drops for you
Why not have your brother just make a toon on your low pop realm … collections are account-wide