Robe colours

[Aratlithiel]

Alatar and Radagast were not the same person

You're right - my mistake. I meant Aiwendil.

Radagast was included by Yavanna for reasons apart from Manwe's reason for the emissaries being sent.It was made clear in Radagast's actions why Yavanna sent him

Quote from UT in the essay of the Istari - "For Radagast, the fourth, became enamoured of the many beasts and birds that dwelt in Middle-earth, and forsook Elves and Men...", and later "...that in becoming enamoured of the wild creatures of Middle-earth Radagast neglected the purpose for which he was sent is perhaps not perfectly in accord with the idea of his being specially chosen by Yavanna."

The council of the Valar was summoned specifically to address the issue of Sauron and choose peers of his to assist in the struggle of Men and Elves against him. Regardless of any hidden motivation Yavanna may have had, Aiwendil/Radagast's task, as appointed to him and the other Istari by the council, was to aid Men and Elves in this struggle. He forsook Men and Elves and therefore failed his task.

He is by no means a 'kid brother'

I'm not trying to insult the guy or anything, but he wasn't necessary or wanted. Aiwendil/Radagast was sent only because Yavanna begged Curuno/Saruman to take him. Manwe did not want five Istari - he wanted three and only allowed Aiwendil/Radagast at the behest of Aule who pleaded his wife's case to Manwe.