If I set up a home web server, will computers that use my wi-fi be vulnerable?

I'm interested in setting up a web server on an old laptop L1. My plan is to connect that laptop to an Ethernet port on my router. I also have another laptop L2 accessing the router via wi-fi. L2 is running Windows 7; I haven't chosen an OS yet for L1 but it will probably be a Linux distro. If someone attacks my website and somehow gains control of L1, can they access L2 as well? I'm trying to figure out how I can use L1 as a laboratory for security testing and web development without putting L2 at risk.