Host discovering problem

Recently I am having a problem with discovering hosts in my local network. Almost 5 devices are connected in my LAN but neither of them are being detected by nmap nor ping is working for them. Only the gateway and the ip of my linux machine is getting detected. Please help me out of this problem

Are you scanning the right place?
For example if i wanted to scan my local network i’d do nmap -O -Pn192.168.1.1/24
-O for Operating system detection