What is best time of year to visit family in Sierra Vista, as far as weather goes?
Weather wise June, July and August are the hottest, but since it is at a higher elevation, it's considerably cooler than here in Phoenx area, with highs typically in the 90's, which is not bad for an AZ summer! Spring and Fall are best times to visit for most moderate temps, winter temps typically in 60s with some dips on the 50s. There is some humidity in summer months, which can make those 90s temp a bit uncomfortable, but nothing like the humidity in SE where you are.
We were there last October visiting friends and the weather was great. Spent a lot of time on the patio as well as exploring Tombstone.
We've been there a couple of different times at the end of March and it was mostly sunny but a bit cool mornings/evenings. Great weather for hiking if that's what you enjoy.
There is no mountainous driving on the route.