@Jonkou888 

"If I turn off the other switches, it turns off the smart switch." means you've wired it wrong.  You should consult with an electrician - you can't wire them correctly unless you know what all of your in wall wires do and no one here can help you without a wiring diagram.

@Jonkou888 

Thanks for reaching out to us. 

Like Mike_P said, your wiring is not correct. Below are some guidance for your reference. If you are not clear about the wiring in your house, it is suggested to consult an electrician.

1> Follow the Setup Video "How to install the Kasa 3-way Light Switch Kit" to and examine the wiring of HS210 step by step.
https://www.tp-link.com/support/download/hs210-kit/
2> Correctly wiring HS210 requires at least 4 lines in each electrical box:
1*Common Wire (Live or Load) ,1* Neutral wire, 2*Traveller Wires ,1*Ground Wire (optional)
(NOTE: If No Neutral Wire is present, HS210 can Not be installed )

• WHITE wire on switch to NEUTRAL wire.
• GREEN wire on switch to green/bare copper GROUND wire.
• Black Screw on the side of switch to COMMON (LIVE/LOAD) wire
• 2 *White Srews on the bottom of switch to 2 *TRAVELLER wires

(NOTE:Please identify COMMON wire as the setup video, examine old Swtich , one Screw would be different color, usually black, that is the common wire )

Here is an instruction for your reference:
https://www.tp-link.com/support/faq/2009/

PS： Yes connected to the switch is 2 travelers(the brass screws) and 1 common(the black screw). you do not need both switches, connect the one switch that has the neutral in the box. Add the white wire from the HS210 to the group of neutrals.