Tips for DMing

Hello! I am running a campaign for my mom and step dad to get into the game. I've had an idea for a slightly One Piece inspired pirate campaign for a while now. Basically, this sea goddess made a magical crown and gave it to a queen. After the queen died, her husband took the crown and got all evil, to put it simply. So the goddess took the crown and removed each gem, scattering the five across a few islands (infinity gauntlet style). It's said that each gem grants the wielder a special ability. The first one gives the user the ability to see magic doors/secret passages. The second allows the user to command water. The third gives the user some sway in terms of charisma abilities, basically gives them advantage on charisma rolls when they use it. The fourth allows the user to communicate with sea creatures/monsters. The fifth is kind of like having a familiar, they can have eyes somewhere else, basically they put the gem in water and they can see whatever area they choose in the reflection of the water. I thought they were pretty cool, but if anyone else has feedback/different ideas, it'd be appreciated!

Another thing, I want the campaign to be pretty lighthearted but have some serious moments. I've always struggled with this as a DM, most of the games I run are pretty grimdark serious stories. I struggled with keeping the silliness under control. I want my mom and step dad to have fun, but I also don't want it to be a train wreck. If anyone has advice on how to manage that, i would appreciate it!! :)