Hide devices connected to WiFi

I’m a noob in home security and networking. I suspect one of my neighbor is sniffing packets destined to my wifi router. I have many questions about this

  1. Will they be able to identify the no. of devices I have connected to the router?
  2. If yes, is there a way for me to hide the device details from packet sniffers?
  3. Will they be able to break my WiFi password if they are aware of web pages I visit regularly. Like a specific youtube channel etc?