I know that chaos all too well — in our house, it’s basically a race to the bathroom every morning. My heater used to give up halfway through the second shower, so someone always ended up yelling about cold water. After one too many freezing mornings, I finally decided to upgrade. I didn’t just grab the first option, though. I found this article:
tankless water heaters and it really helped me figure out what size and type would work best for multiple back-to-back showers. Definitely worth a read before you choose.