There's a
cursory pronunciation guide for Seeker prefixes in the Race Naming Conventions thread. So, based on that, it should be "yah-SHTO-la" and "goo-RA-ha" respectively (or "goo-RAH-a", perhaps; the pronunciation for given names isn't detailed, except to say that aitches are usually unvoiced by non-Miqo'te because of their peculiarity -- and with that in mind, it's possible that the "sh" in "shtola" wouldn't be pronounced as a digraph in the Miqo'te language either, but that's neither here nor there).
Some actors get close enough with "yeh-" or "yuh-SHTO-la", which really doesn't bother me much, but you'll hear
others say "ish-TO-la" (following the pronunciation logic used for "Ysayle").
Conversely, there's at least an internal consistency to the pronunciation of "G'raha" in the dub that makes that change a lot more palatable to me, since although it's different, the difference is always the same. But would I like to hear the "proper" pronunciation? Yes lol.
All that said, I do have one gripe with the aforementioned pronunciation guide, and that's its treatment of F. If I'm understanding correctly, we're told it works the same way the dub treats the prefix in "G'raha", where it simply merges with the first syllable of the given name. It works for a name like F'lhammin, or with any given name that starts with a vowel, or R, Y, or W, but that's it. Try to say "fsteak" lol.