Sprinkler valves are surrounded by tree roots
Literally working on a similar problem, minus the gigantic roots...

The problem with the roots is the roots: if you work around them, you work around them. If you cut them, you may kill the tree, which is a whole nother ball of wax.

Before you dive into the roots or replacing valves, consider just checking the valves for simple issues and troubleshooting around those principles. There are a plethora of videos on "how to fix a leaking sprinkler valve" - try some of those; if you have a screwdriver and won't melt from getting wet, the experience can provide a wealth of information just by diving in. This one is descriptive and educational - it might not solve your problem, but might give you enough insight to narrow your search. Worst case scenario, you break something and hire the professional you were going to hire anyway to install a new valve.

TL;DR: Troubleshoot the valves with online videos. It's not as scary as it sounds.