After putting this aside for three months, I finally spent another few minutes thinking what the last line can mean.
The B section:
Starting off from the part that's harder to break apart, I'm seeing "Helelele lelele" as one word or just one gesture (maybe similar to dokidoki in Japanese). Its repetitiveness to me sounds like some kind of invitation, which leads to "let the journey begin". Let's just say it does mean that, then I can translate it into something like "come, come" in English.
Now the first sentence in B. Carrying the structure I established in section A, the second "holo" in "Holo-ohlo holo forðe-holo" should be a pronoun. With the next sentence being an invitational gesture, this one should be about something inviting someone.
This invitation obviously has to be towards the Abyss, since the character in the song answered it by starting a journey that way. So one of holo-ohlo and forðe-holo has to mean "towards the Abyss".
Putting that aside for a bit, focusing on the word "holo": if "holo" is a pronoun, the only sensible entity that would do the "invitation" is the Abyss itself, or a God of the Abyss. According to what Nanachi said [ep13], the religion of the Abyss does not involve another entity that represents the Abyss, therefore "holo" should mean "the Abyss".
But why not "Hanezeve"? I'm thinking maybe "holo" can mean "it", albeit in a holy form. I'm borrowing this idea from the Mandarin word "祂", which is exactly "it" for gods.
holo: modifier, "holy", "Abyss", and/or "itself"; pronoun, it (holy form, like "祂" in Mandarin)
Now each of "holo-ohlo" and "forðe-holo" has to mean either "invite" or "towards-abyss" / "towards-itself". Following the structure of "cara-dhina" = "in-deep", I think "forðe-holo" is more suited for "towards-itself", with the preposition in front. Then "holo-ohlo" would be something like "holy-invite".
forðe-holo: towards-abyss or towards-itself
So the rough translation is now:
Full "translation" with made-up language and grammar
Hanezeve Caradhina / Deep in the Abyss
Listen to Hanezeve Caradhina (and the rest of the Made in Abyss OST) on Spotify.