That’s looking Sweet! You have skills, so it is not really hard to believe you accomplished 4 game prototypes solo. UnrealEngine makes this possible.
A 4-in-1 Game is possible. RPGs do it all the time with Mini-games. You can also see this in Hybrid Games using a variety of game mechanics from different genres. Its all about designing modular subsystems to be used in multiple game styles. This notion is what a All-Perspectives-In-One Camera System like V8 Supercam was developed to solve.
Because I’m a solo dev, to reduce my workload, I actively seek out the common features between Game Mechanics in different game styles and design ‘generic’ subsystems to be shared amongst them. I consolidate features and repurpose subsystems for uses they may have not initially designed for.
For example, a Projectile weapon functions nearly the same in all perspectives and styles. Casting a Fireball, Shooting a Bullet/Arrow, Launching a Missile, Power Punching, Sword Swinging can all Spawn a Projectile to inflict Damage/Physics Force upon Collision. So, I designing a single Projectile System (TRAJECTILES) to be used amongst them.
Thus, the Railshooter (kill all), Third Person (Hack and Slash action adventure), Top Down (Space theme) and a Shmup can all use the same Projectile System so you only need to develop one Weapon System.
Aliens & Zombies go hand in hand.