If I'm reading that diagram correctly the coaches had seats only 34 inches wide (2 feet 10), surprising on cars 8 feet 5inches wide overall. It would've allowed for a wide aisle (no doubt appreciated by crews) but that seat width isn't really sufficient to be considered comfortable for normal-size people even of that era**. Most roads opted for somewhat wider seats with a narrower aisle; the D&RG had 35 inch seats (still quite "cozy") on only an 8 foot outside width. If didn't misread the diagram then I'd have put them on my short list for conversion to parlor cars, too.
**Such seats would of course be satisfactory in a low-traffic environment where trains were usually running at much lower than maximum capacity, as was quite often the case on many minor little roads. For the sake of comparison, a generic modern school bus usually has about a 38 or 39 inch seat width, typically with a very narrow aisle on an overall interior width roughly equivalent to these old 3 foot gauge coaches. Such trade-offs are inevitable when the loading gauge is restricted.