Can I Read Data from Devices Connected to My Home Network?
If your Wi-Fi network is using WEP, WPA-PSK, or WPA2-PSK for security, then, yes, anybody who knows the password can decrypt traffic from other users. Of course, any traffic that has another layer of encryption (HTTPS, ssh, etc.) will not be readable.
If the network uses WPA3, then it is much more difficult to do so, probably not within the capability of the average attacker.
In either case, you should set up a separate guest network for any outsiders (many routers allow this). Not only does this prevent them from spying on you, but also it mitigates other problems such as people with infected devices connecting to your network and introducing malware into your home network.