Where is the sutra source of Buddha[s] (plural) existing and blessing peoples minds?

Tibetan/Mahayana Buddhists believe in such a thing, that somehow specific Buddhas exist....somewhere and emanate in forms in the world and are able to bless other peoples minds. My question is where does the source of this info come from? I have never read any such things from the Buddhas teachings (though I am not a scholar who has studied all sutras) though from the maha-parinibbana sutta Buddha explained "where" he will go after death and it is nowhere, as in not to another form as the causes to arise again have ceased. So how can there be Buddhas that exist in other realms of existence that bless peoples mind? Unless of course these beings exist in realms or worlds now, but that creates another conundrum as to how human beings communicated with them. Buddha did explain in MN115 that no 2 Buddhas will exist in the same world system at the same time. I would like to know the source of this belief, and I guess I am also asking is this just some cultural belief system that is not actually the Buddhas teachings, like dharma protectors for eg.