Most likely lesser, as they are the Jardines subspecies most commonly seen in the US. The greater is larger and remains more green whereas most lessers get more of an extensive orange forehead after maturity.
One does and one doesn't. Robin my older Red Bellied is a "typical" Poicephalus and hates all others birds. He will viciously attack and cause harm if given the chance.
Griffin the Ruppell's is bonded with Raven my Pionus. The Pionus is at least twice the size of my Ruppell's, but they are an odd couple lol. They do have different temperaments too. The species are from completely different continents and habitats, and are completely different in personality, size, looks, etc. but somehow it just works with these two individuals. Keep in mind many Poicephalus don't tolerate other birds. They're also one genus that's notorious for becoming one person birds. I love them though.