Which app to see other phone screen in real time works?

@Nooneshere, thank you for explaining all that… it sounds so complicated for someone like me who barely knows how to use my own phone. Sorry if this is obvious, but could you tell me more about Spynger? Is it easy for a grandma to set up if I just want to check what my grandkids are doing online without them getting into trouble? I worry about them all the time, you know… Does it really work without a lot of fuss? I’d appreciate any simple steps.