My father is so polite. [new sentence!] I’m trying to catch some of that trait from him. When he goes to a local traditional market, which usually has elderly vendors, he buys from all of the workers so that none feel [subjunctive mood!] bad or ignored. Don’t get me wrong. [new sentence!] He doesn’t buy from every single seller in the bazaar, but when he wants to buy a specific thing, like watermelon, he'll buy three, all from different sellers. He is considerate and kindhearted, and I hope some of that rubs off on me. I'm not sure what you mean by "he take three ones ...." Since he buys 3 watermelons, you can say "watermelon" or "watermelons", but not "a watermelon". Sentences are separated by periods, not commas. If you want to join two sentences into one, use a conjunction.