This is … quite an ask, I must admit. So to begin, I’m afraid I can’t offer care tips for six vastly different pokémon in a small amount of space, so I’ll simply offer this as a general tip: read up on each pokémon species to get hints about their basic needs. For example, treecko is a tropical insectivore, so it will need a moist environment and a largely insect-based diet. While you could possibly double up on habitats or diets for like pokémon, it’s also worth it to be aware that two pokémon, as alike as they may be, might actually have different needs. (Turtwig is an herbivore, and snivy needs larger prey, like feeder mice.)
If you’re out on the road and these are meant to be your starters for a journey, it might be easier to care for all of them (that’s what kibble and general care facilities at pokémon centers are for), but if you live at home, a team this diverse might be difficult unless you have a lot of space and money. If it is difficult, consider leaving a few at a shelter or rehoming them. This goes especially if you plan on evolving them, as their needs—not only for space but also basics—will increase exponentially. It’s not impossible to house six fully evolved starters if you’re not a trainer, but it’s difficult. And, well. Expensive.
As for your avian pokémon fighting one another, most bird-like species are actually highly social, so it’s more likely that they’ll form a flock (and perhaps try to rope in some of the reptiles while they’re at it), especially once they understand they’re part of the same team. The others, meanwhile … generally, you shouldn’t have a problem because in most cases, starters are bred to be amicable with other pokémon, but keep an eye on that treecko and snivy.
Best of luck!