Do they?
You mean, like if I had a guest on with me, and they died 200 times would it give the original account 200 deaths?
Probably not.
No they dont because it activates a separate account for the guest so it doesnt use your own
No. That wouldn’t be very fair. If you were playing with a friend who had never played Halo before, your K/D would really suffer!
No, any stats for guest accounts don’t affect your K/D at all.