@Mischa If you don't need to fully use Franklin but only need it's look instead, you can switch or change your model to Franklin, then use https://www.gta5-mods.com/scripts/character-swap mod to change your ped hash to Mikey. You will play as Frankie boi but the game will think you playing as Mikey and you can play tennis.

I wish wish though someone make a tennis court mod in a better location that you can play tennis. I mean sure it's nicey the fancy to have a small tennis court at your backyard but the scenery of it ain't nice.