If I am playing Volibear legend, and I play Seraphic Wyvern. Volibear legend triggers and Seraphic Wyvern trigger, Does the 1 rune channels ready plus 1 rune exhausted, or are both runes channelled exhausted?

No — both runes enter exhausted, not one ready plus one exhausted.

Volibear's ability generates a channel event that already carries the "exhausted" stipulation, and Seraphic Wyvern's replacement inherits modifications from the effect that generated the event (Rule 375 — same as its Gold-token example, where the additional token also enters exhausted). So Volibear's "channel 1 rune exhausted" becomes "channel 2 runes, both exhausted": you get the base rune exhausted and Seraphic Wyvern's extra rune exhausted, total 2 runes with none ready.

The one thing to watch is that Seraphic Wyvern must still be on the board when Volibear's trigger resolves (channeling happens on resolution, not at trigger) — if your opponent kills it in response, you're back to just 1 exhausted rune.