Thanks for using JA
You can replace one tire as long it's the same brand and model tire. the difference with tire brands is that they have different circumference even if they have the same size.
thread depth and wear isn't an issue.
Just to be sure, the manufacturer has no "tread depth criteria", right?
to be specific tires are no good at 2/32 of an inch, between 2/32 at 4/32 a replacement is recommended anything above that is a decent tire.