I think the Spawn thing is a red-herring, so its not at all surprising that it is confusing. At first it looks like town gets a nifty tool in being able to kill two players in one cycle. But the Spawn mechanic pretty much negates that benefit.
In my opinion, Town should lyse the one and only Spawn every Summer and lyse one Player. I can only see very narrow and unlikely scenarios where lysing two players makes sense. That case is where two players are both known to be scum and are believe to possess Winter Actions. Other than that, I see no reason to lyse two players during Summer.
Well, I can think of one, but I discount it as a possibility:
If there exists a vigilante type town player who can kill spawn during winter, then killing two players and leaving spawn alive for winter makes sense. Town Kills two players and the Vig kills the Spawn during Winter. Yay! However, I discount this possibility because the benefit is so large that it is unbalancing. In other words, a spawn killing town role is so powerful, I don’t believe it exists.
In summary, every Summer that the game is not over, a new Spawn spawns. That means for every Summer we must lyse one Spawn on average. If we skip lyseing a spawn one summer then we MUST lyse TWO spawn during a subsequent summer. Therefore, there is little reason not to simply lyse one spawn every Summer.
What does this mean for the game? On the surface not much. But! It totally sucks for town:
In a typical game, endgame is 1 scum versus 2 town. This is the ultimate endgame situation. The slight variant, 1 scum versus 3 town, is also endgame, but converts to 1v2 with a Town-led NO LYNCH.
Anyway, in THIS game, with spawn, we can never get to 1v2 without losing because every summer begins with a new spawn. Yikes! That means a summer with 1 scum and 2 town is a scum win (1 scum + 1 spawn).
So a Summer with 1 scum and 3 town is the ultimate endgame situation. 1 scum and 4 town is also endgame, but converts to 1v3 with a town led Lynch Spawn and No Lynch… which I’m not even sure is possible since the option to vote no lynch is not included in the rules and the spawn will randomly vote anyway.
So in the end the entire spawn thing boils down to a standard game where the scum win condition is slightly earlier.
That is, assuming Town doesn’t have Winter actions that can eliminate Spawn. But as I stated earlier, such a mechanic is overly-powerful for Town.