It's a good start! The concept is there and what you had was good.
Unfortunately it was a bit unclear what was happening when I started. Once I figured it out it made much more sense, but some key elements were still missing. It took some experimenting to figure out how to build farms, and the cost of the two NPCs should really be shown to the player from the beginning.
The sound design and pixel art are simple but really good! Some music to compliment them would have been a welcome addition as well.
It's a good game, it just lacks a few things here-and-there that would add a lot to the experience. With a bit more work this could be a really fun little minigame!
(If you do decide to continue this in the future, I'd also suggest adding more NPC types that could have strengths and weaknesses, like an archer with less health but more range!)