We have won our first 7 wars in a row but now we are about to lose. Will it reduce our clan XP? Also, is there any other way that our clan XP can be reduced?
No, it is not possible to lose clan XP in any way.
On the contrary, you will still gain XP from your efforts in your war. The only clan XP which is not awarded if you lose is the war win bonus of +50 XP. All other XP gained, for instance from destroying bases and reaching star goals, is still awarded.
As such, if you lose you will still be very profitable when it comes to clan XP. You just miss out on the +50 win bonus.