Rusty and Jonas Jr are Fraternal Twins, conceived the same night (a Venture's orgy) within the same mother's womb but having a different father each (this is possible, look it up).

Ok, so this is what happened. Jonas Venture Jr and Rusty Venture are fraternal twins, each having a different father (it is possible, look it up). As it was mentioned in one of the previous comments, this was a product of one of those infamous Venture orgies. So the original Blue Mod is father of Rusty and the…