Mostly. If you want to say they are ALSO fun/funny, I would suggest adding the word "aussi" (which means also) after the word "mais" to make it perfect. So you'd have: Ils sont <span>sérieux mais aussi amusants.
Besides that one word you might want to consider adding, your sentence is grammatically correct!</span>
Un jour de marche est le samedi. Il y a beaucoup de personnes au marché. Tout le monde achète des ingrédients pour préparer de la nourriture à la maison
