Red: Pikachu - Starter, default in Yellow Blastoise - Received as a Squirtle in Vermillion City Charizard - Received as a Charmander on Route 24 Venasaur - Received as a Bulbasaur in Cerulean City Snorlax - Encountered blocking Route 12/16 Lapras - Received at Silph Co
Ethan: Typhlosion - Starter, most media shows Gold choosing Cyndaquil Togekiss - Received as a Togepi from an Egg Shuckle - Received in Cianwood City Dragonite - Received as a Dratini in Dragons Den Hitmontop - Received as a Tyrogue at Mt Mortar, Top is the Johto evolution Sudowoodo - Encountered blocking Route 36
Brendan: Swampert - Starter, most media shows Brendan choosing Mudkip Wobbuffet - Received as a Wynaut from an Egg Castform - Received at the Weather Institute Metagross - Received as a Beldum from Steven Kecleon - Encountered hiding on Route 119 Smeargle - Found in Artisan Cave (cave with nothing but Smeargle)
Lucas: Torterra - Starter, most media shows Lucas choosing Turtwig Blissey - Received as a Happiny from an Egg Lucario - Received as a Riolu from an Egg Togekiss - Received as a Togepi from an Egg Porygon Z - Received in Veilstone City as a Porygon Rotom - Encountered in the Old Chateau
Hilbert: Emboar - Starter, most media shows Hilbert choosing Tepig Simisage - Received as a Pansage at the Dreamyard Volcarona - Received as a Larvesta from an Egg Zoroark - Received as a Zorua in Castelia City Darmanitan - Encountered in Zen Mode at Relic Castle Entrance Musharna - Encountered in the Dreamyard Underground
Nate: Emboar - Starter. most media shows Nate choosing Tepig Sawsbuck - Received at the Weather Institute as a Deerling Blissey - Recieved as a Happiny from an Egg Shiny Garchomp - Received as a Gible in Floccesy Town (male and black 2 come before female and white 2) Zoroark - Recieved as a Zorua in Drifveil City Gyarados - Bought as a Magickarp on Marvellous Bridge
They're excellent "only one starter" teams for the later NPCs, but I'd make some changes:
Ethan: Red Gyarados over Dragonite. Unlike the Dratini it MUST be encountered to progress the story.
Brendan: Electrode over Smeargle. Smeargle's a bit forced, especially since Sudowoodo must be caught or defeated in order to see Smeargle. He could have encountered Electrode in Aqua's Hideout at Lilycove.
Lucas: Drifblim over Togekiss. Mostly because Ethan already has one, which was the reason you avoided Sudowoodo on Brendan, right? Drifblim could have been caught as a Drifloon at Valley Windworks.
Hilbert's team is good enough, but Nate should have something else besides the version-exclusive Garchomp. I can't think of anything, admittedly, and since it seems you're trying hard to avoid Eevee...