First, both Tyranitar and Tangrowth are obtainable before the first time you battle Lance.
Second, if you want to defeat Red as quickly and effortlessly as possible, then I recommend using only Typhlosion, Ampharos, and Slowbro. Crobat covers only Venusaur, which Typhlosion covers better. Grass Pokemon cover only Blastoise and Lapras, which Ampharos covers better. Umbreon doesn't cover anything. A team of 3 Pokemon will level up a lot faster than a team of 6 Pokemon.
Third, if you want to defeat Red as quickly and effortlessly as possible using a team of 6, then I recommend keeping your 6 high-level Pokemon. Leveling up a low-level Pokemon takes a lot of time.