I’ve just looked up “Brown Dwarf” on wikipedia, and was redirected to REd Dwarf stars via https://en.wikipedia.org/wiki/Luhman_16 and thence to https://en.wikipedia.org/wiki/Stellar_classification
In this latter article, there is an extended Treatise concerning all forms of Stellar Classification, not just the traditional OBAFGKM [Mnemonic: “O, Be A Fine Girl, Kiss Me”; “Girl”, on account of the fact that, at the time, almost all Astronomers were men]. The article, under the heading of L-Class stars, tells that the largest of these Stars are capable of fusion, but they are very cool, radiating mostly in the Infra-red - their surface temperature is around 1100 degrees Centigrade or so. Such a star would look dull red, possibly crimson or brownish, and the Habitable Zone would be very close to the star, making it [the star] appear large in the Sky.
An alternative set-up might be the “Falcons of Narabedla” / Darkover set-up [cf. the truly brilliant “Darkover” series by the late, great, Marion Zimmer Bradley]. This would allow for a Planet to orbit a really cool [temperature-wise] Red Giant star of some type. The only problem here is that the cooler the Giant Star, the larger it is, and thus the dramatically longer it takes for a planet to orbit it.
It should also be noted as a parallel, that Oerth [the Planet of Greyhawk, Blackmoor, and Kara-Tur], has two dissimilar-sized Moons, just like Athas. Is Athas a late [and possibly Alternate Prime] version of Oerth?