Can I point out something? Since the couple must be made in CAS, there can't be any alien babies since aliens cannot be made in CAS and you can't turn a human into an alien. The only way you can have alien babies is by alien abduction or moving in an alien, the latter would violate the rules, so only an accidental alien abduction would bring an alien into the house. So that rule about aliens maxing another skill should not be in there as there is no way for your couple to have an alien baby. You'd have to send alien babies to their homeworld.
Mermaid kids are possible if you buy mermaidic kelp or get it from a mermaid but not aliens, you can only get aliens from in-game so there is no point in having the rule about aliens needing to master another skill as there will be no alien babies in the challenge unless your male Sim gets abducted.
It actually is possible to create an alien in CAS. If you save a YA alien character to the Sim Bin, and that character appears when you first open CAS, then the character will remain an alien. It's doable, but it takes a lot of patience and/or luck.
That said, I'm not sure why aliens wouldn't be able to use the Future Technology skill, since they don't get any bonuses to learning it or anything. Sims with the Future Sim hidden trait will have it automatically maxed, but not aliens.
EDIT: I have some questions regarding the auto-placed lots in most towns. Is it okay to leave those there, or do we need to delete them? If you can leave them there, then that's a serious disadvantage for players starting in the newer store towns. Similarly, can we leave the empty small parks in Moonlight Falls as they are, or do we need to switch them to empty lots?
Finally, this is probably just a matter of laziness on my part, but I'm not entirely sure I get the edit town instructions. Do we have to fill up all the empty lots with houses, and then go and bulldoze five of the houses we just placed in order to make the five edits? Would it be okay to reverse the process - do whatever you want with up to five lots, and then fill up the rest with houses?