It's possible but honestly, who would really care if Insuku made a Sister Travel remake (or Sister Explorer if that's what is intended to be the remake) and changed some details instead of making it an parallel universe or some other excuse?
Who is going to riot because the guild girl (Aidelle) is now actually the Imouto from this game? How many Aidelle fans are there really?
I haven't played the DLC yet so I might be missing details on how Intimate the characters are but:
Same with Kana, just hand-wave her and brother never having sex as uncertainty on her part about her femininity or embarrassment about sexual acts in general, and viola! We're back in business.
Yui can easily replace Medico (if Inusuku is lazy and doesn't want to design a new character). They basically LOOK the same, Yui would even have an easy excuse for her delay in joining the group "I got so loney without you and Kana that I decided to follow along afterwards!" or they can say that the Imouto or Brother secretly sent Yui a letter asking for her to help - because the guild needs a skilled medic.
Kasumi could make a cameo as an npc or replace the Sister Travel mage (or we could have two mages with different specialties, whatever).
Same with Yukari the Elf, she could be an NPC or never show up in the Sister Travel Remake- She's probably used to humans dying or moving away.
EDIT: and power level stuff... I guess they could do what Rance does and say Brother and Kana got rusty for some reason between adventures... or that the creatures where they are now are much stronger (Inusuku could even skip doing rats, boars, slimes and start with more dangerous looking monsters at the beginning of the game) or they could say Brother and Kana are under a curse or that the a new"Demon King's" influence has made all creatures hostile to humanity stronger.