I would try to keep Caterpie closely related to Venonat and Venomoth. The programming-error "crack" theory actually aesthetically makes some sense, and I think fans would appreciate a call-back referencing the similarities.
Durant is based off of ants Beedril is based off of wasps Vespiquen/combee are based off of bees Ant : [link] Wasp : [link] Bee : [link] All 3 are suborder Apocrita (which consists of wasps, bees and ants. more info here ) according to this information, but ants and most wasps are under the superfamily Vespodia (which contains social wasp families and ant families, but no bee faimlies. more info here [link] ) whereas bees fall under the superfamily Apodia ([link]) then again, beedrill and vespiquen do have quite a few traits of the other (especially vespiquen). This leads me to consider that maybe all three have an equidistant meeting point, and said bee/wasp ancestor to contain traits of all 3 mons right?
ooh i like how there are some traits you can see in the sprites that show you where other insect pokemon not included here would go, like the Yanma wings on the Beedrill anscestors and the obvious Caterpie and Metapod traits on second set of ancsestors. Although i'm curious to see how you're going to fit Venonat where it appears to go, not questioning the choice, just think it will be interesting to see the result