I've gotten a clearer idea of the linguistic situation here. Apart from Kwarandjie, which, as I've said, is the main language of three of the four villages (and used to be the lingua franca of the oasis), and of course Arabic, there are a few families here (in Ifrenyu and el-Karti) speaking Tamazight - specifically, the dialects of the Ayt Khebbach and Ayt Atta tribes of southern Morocco. They seem to have traditionally been nomads in the general vicinity who settled down here in the seventies or so, although much outnumbered by the (Hassaniya Arabic speaking) Rgaybat who constitute what little population there is in the desert surrounding Tabelbala. I've been doing a little fieldwork with them, focusing on vocabulary that might be relevant to Kwarandjie etymologies, and have been struck by how rarely they seem to provide the source for Kwarandjie's Berber vocabulary - even when the word is quite common in Berber (as it often is not), like adra for "mountain", they seem to use a different one (in this case, tawrirt). The speakers I've spoken to have a rather impressively large vocabulary, but often seem quite embarrassed to speak the language at all - one at first quoted me a local proverb "Esshelha ma hi klam, weddhen ma hu lidam" - Shelha isn't language like ghee isn't (some sort of highly valued medicinal fat product.)"
The list of tense/aspect/mood particles continue to grow - a particularly impressive example I encountered yesterday was `a-s-a`a-m-k-dri (1S-neg-prox.fut.-subj.-yet-go), meaning something like "I've totally stopped going." (ma tlitsh nruh kamel). Actually, -s-a`a-m is a contraction that probably deserves a single lexical entry, but never mind. Note the `ayns in historic Songhay vocabulary here, deriving from original gh.
The phonological issues I mentioned last turn out to derive historically from deletion of an emphatic r, not from any significant difference in the consonants themselves. Not sure yet how to deal with them synchronically, though...