These three games are highly anticipated what game has the most potential to come out first, second and which game will be last?

Theres a lot of rumors running around that HL3 might launch of the Gabecube. Because this is a hot rumor HL3 is my first pick, followed by GTA6 and lastly TESVI. 

GTA VI before TES easily.

Half-Life though could easily drop first half of next year. I'm expecting a half life game to be announced within the next few months and to launch very soon after the announcement.

Yeah, what he ^said.

TES VI is too big to be shadow dropped, and Bethesda has said many times that it will still be years before it comes out. No doubt about these two.

Valve, on the other hand, is kind of weird and like to make things in their own special way. Who knows, HL3 may never come out or it may come alongside the launch of the new Steam Machines, maybe even bundled together to move more units. You never know with them.

Skeptical on Half-Life 3 due to how long it's been, and TES VI is still a long way away.
GTA VI will make its release date or will very likely launch in 2027. I don't see 2028 or later on the table.
Half-Life 3: Holiday 2027, not a launch title for the upcoming Steam Machine
TES VI: Holiday 2030

Do we really need to give any benefit of the doubt to Bethesda with how the development cycles have gone during these last years ? Heck for all we know. TESVI isn't before 2030 at least.

I see more chance in seeing the rest of the list release first for sure