So I have a question. If I donate $16, does that mean that I get everything that is at the $16 Tier and below or just the $16 Tier? By that I mean, if I want to have early access to both games, do I need to donate $8 for Demon's Dream: Collector Edition, and then donate $16 for Muscle Management Remake: Collectors Edition, or will the $16 donation gift me both when they become available?

You get everything(all the other tiers) bellow your tier yes! So if you pay 16 you get both game.