Others can not join me when I open my hotspot

Maybe your hotspot have a password. Have you checked?

If you already checked that they entered the correct password, you can read this article: If Personal Hotspot is not working on your iPhone or iPad (Wi-Fi + Cellular)

Any devices joining your WiFi hotspot will require your WiFi hotspot password. You may be restricted in the number of device connections that can be made to your device; the maximum number of simultaneous connections can be determined from the subnet mask used by your hotspot network settings.