This is a very interesting project, and I shall keep a eye upon it.
Now, let me give some small criticism, if I may:
-Please, pretty please, it's a very small thing, but as I understand it, the "spaniard" word has a sort of derogatory connotation. I really hope the culture is called Spanish at the end
-What is the rationale behind the fantasy skintones?
-and lastly, I concur that references to well-known sci-fi settings should be keep subtler.
Now, the following is just some random thoughts into world-building that may or may not be of use, but that I had when reading the description of what you have so far in the way of lore:
I get pretty much that you are going for a "medieval Mars" feeling, and that the "lore" justification for it is pretty secondary, but I think that having a more solid background can only help give personality, depth and cohesion to the mod's world, for example:
How long into the future did colonisation start? That might have influenced how the initial colonial projects were laid out, and the amount of population devoted to it. For example, It is most likely that entities like an European union, or any other federation of middle-rank individual states would have led a joint colonisation program. Thus it would be more likely to see mixed european (or say, middle eastern) culture and ethnicity than, say, mixing of american and chinese cultures. It also would influence the plausibility of a multicultural state founding several diferently-cultured colonies. Concretely, If, say China had the ethnic policy it had centuries ago, it probably would only have colonised with it's main culture, or have an elite ruling culture over a subservient majority culture. I actually don't know what is the current or the plausibly future policy of China, but the plausibility of having two different chinese ethinal colonies come into play.
-How long lasted the colonial period prior to the eruption? That would determine things like historical relationships between colonies. As a rule of thumb, the more time the colonies lasted, the more freedom you have to set their "personalities" as diferent from their metropoli. (so, after centuries, perhaps the kurdish descendant are not so begrudging against the turkish ones, but the european cooperation spirit has banished?
-How dependent were the colonies with respect to Earth? If they became autonomous states, that would have given even more liberty to depart from current state of the world. This also could influence the political and cultural map. One could presume that the earth great powers which started the colonisation at roughly the same time did divide the areas of influence roughly equitatively, perhaps with the late-comers getting poorer or smaller regions.
-Really, how much of the technological cultural and historical knowledge has been lost? Going "plain middle age" can be less interesting that mixing elements. Say, for example, that elemental unterstanding of steam machinery or mechanical works has remained more or less preserved, but there is not enough manpower to produce enough machinery to automatise agriculture. That would have rendered a society where more or less advanced artiluges (clockwork engineering, semi-mechanised water distribution, as some examples) can be implemented by specialised artisans in big and rich urban areas, but the rural landscape is basically medieval. Or considerr the state of technology in post-apocalitpic worlds such as that of "Mad max": knowdledge of use and reparation remains, but not of new production, and there is some resource that is too precious. Having some sort of technological edge can come into play specially if you are going to have a modern warfare invasion from Earth
-What is exactly the nature and reach of the disaster? What are the population figures? Have all areas and different groups been equally affected? Is all the land populated, or say, is there space for a second colonisation to stablish new settlements outside the current martian states boundaries?