Denzel looks up to Cloud quite a bit and even tries to fight off some of the monsters (fighter role).Nothing in AC implies "OH HEY DENZEL AND MARLENE ARE JUST LIKE CLOUD AND AERIS AND OH THEY'RE GONNA BE FUTURE HEROES AND MAIN CHARACTERS".
Marlene's got her hair done up almost like Aeris had hers, takes care of Denzel (healer role), and senses/sees Aeris.
It's not a lot, but it is there. They're not mini-me's of Cloud & Aeris, but there are parallels there. I'm not even trying to say it's definitive proof that they'd ever star in their own game. I don't even like the idea. I just thought it was an interesting idea to consider.