Old IPhone
Will logging in to my old iPhone alert my new iPhone in anyway?
I let my brother use my old iPhone and I’m still logged in on everything. Will he be able to see all of stuff? Will it even notify me cause it’s a recognized device?
Question marked as
if you're going to let someone else use your old phone, and you have concerns about your data, etc.. then you should erase it before letting him use it
What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support
If he has it now and it's still signed in with your Apple ID, then there are certainly things that he could access that you may not want him to