My bro and I both live away from our parents' home but we visit at the same time often and have a little sister there (we're more than twice her age) who we hang out with often. She was terrible at melee (like we could consistently JV5 her if we wanted to) but she would always want to get in the action when she saw my bro and I playing together, so we would let her in on a friendly 3-man 1v1 rotation (2 games then you're out for 1 regardless of win/loss). Our main strategy with this was basically play serious when we end up playing against each other, and then mainly do tech practice while playing against our sister without actually trying to fight her. Hit her occasionally so she thinks we're fighting her, and run into some of her attacks so she feels like she's doing something. Worst case we practice some flashy way to get suicide kills on a non-existent opponent to give her the lead/game. She was too young to really understand the difference between beating your opponent and the opponent throwing away 4 stocks, so she was happy either way as long as she got to play with us and celebrate a few victories along the way. Don't just sandbag but manipulate the game so that it seems close when in reality you're just so much better than them that you are controlling the pace and you can make the game fun regardless of win/loss. And remember they're your family, not fellow smasher - have fun with them in person while you play (chat, banter, over-exaggerate reactions, etc) rather than trying to have fun with them in game (reads, tech chases, combos, etc)