Internet problems… IPad and ps4 won't connect?

I noticed it this morning when my iPad was acting up… I disconnected from the Internet and tried logging back in but after a few min my iPad would disconnect from the wifi and make me log in again and sometimes say the password was wrong even tho I know it was right… I noticed it kicked me when I opened the PlayStation app or if I let it turn off… Then I go to my PlayStation at night and it doesn't wana connect either… They both show my internet but have trouble connecting… Please help ive had this problem all day I disconnected my router and modem I restarted and reset my iPad but I keep getting this problem. I've even changed the wifi password a few time and I can connect but it kicks me out a few min later I went over to my sisters place and the wifi works fine there it's just mine… Some people say I need a firm ware update on my router but idk how to do that and if it's not that what could it be? Please help I have a linksys router and I'm using xfinity Internet
Added (1). My other iPad xbox and phone work fine

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