To answer some of these, it is necessary to go into different languages
Viola ---> Viola
Before you ask YOU WOT MATE listen to this;
The name "Viola" is also the name of a type of Butterfly, a genus of "Skippers". This immediately relates to Vivillion as well as Viola's gym type, Bug. You could also make a slight connection between the words "Violet" and "Viola", and somehow relate Violet which is a colour, to Viola's love for photography.
Viola is also a type of flower, which coincides with her sister's Japanese name, Pansy, another type of flower.
Grant ---> Granite
In addition to this, the Japanese name is ザクロ (Zakuro). This is derived from 石榴 (Zakuro - pronounced the same way) which means Pomegranate and also contains the character "石" (Isshi) meaning Rock (Which is coincidentally his gym type). So you have a pun on Pomegranates and Rocks there.
The French and German name "Lino" also seems to draw from Linum which is a genus of flax.
Korrina --> K.O + Arena
Split that name into two parts:
Ko and Rrina
Notice how Ko can be taken as K.O and Rrina sounds like Arena a little bit - both of those words refer to fighting (Knockout and (fighting) Arena), which is her gym type.
However, her Japanese name, Korni, means gherkin, and is basically a pun with her grandfather's name, which is Concombre in Japanese... which is cucumber in French. I personally think it's because parts of their hair resemble gherkins. (ed: fondant)
Ramos ---> Ramus
What the hell does Ramus mean?
It's Latin for Branch. And guess what, Ramos runs a grass type gym.
The Japanese name, フクジ (Fukuji) also derives from 福寿草 (Fukujuso) meaning Pheasant's Eye, which refers to the plant, Adonis.
Clemont ---> Lemon Battery
Closest possible thing I found. Battery --> Electricity :D? And I think you've all heard of "Lemon Battery"before.
The Japanese name シトロン (Citron) appears to derive from the French word "Citron" meaning lemon - possible reference to Lemon Battery. Lemons are also yellow and the Electric type is often associated with the colour yellow.
But let's step out of these languages, and for this time go to Chinese (Mandarin)
His name in Mandarin is 希特隆 (Xitelong). The last bit "隆" (long) could refer to 隆隆 (longlong) which is a Chinese onomatopoeia for thunder rumbling. (Actually it's really just the transliteration, no one uses 隆隆 to describe thunder. Really. ed: fondant)
Valerie ---> Faerie
Similar spelling at the end, and faerie is another way of saying... yup, you guessed it, Fairy!
Furthermore, the Japanese name "マーシュ" (Mache) possibly draws inspiration from the word 魔術 (majutsu) meaning Magic. Mache is also the French word for Corn Salad, which can also be called "Rapunzel" in certain other languages - and Rapunzel is a fairy tale story.
Olympia --> Olympian
Olympians were the gods of Olympus - they were "celestial". I suppose it is possible to refer the word Celestial to "Psychic" in a very narrow sense, but that's the only thing it really seems to draw from.
Wulfric --> Wolf + Frigid
The name "Wulfric" can be taken as a possible combination between Wolf and Frigid. Wolves normally live in icy areas. Frigid means cold. Ice is cold. Yay.
The Japanese spelling ウルップ also draws inspiration from ウルフ (urufu) which means wolf in Japanese.