"Those of" will always be followed by "who" "Those of...who..." If there isn't a "who", use "some of" "those of...who..." and "some of...who..." have different meanings. "Those of them who protested were killed" means that some of them protested and some of them didn't, but everyone who protested was killed. ( for example, 50% didn't protest and lived, and 50% protested and were killed) "Some of them who protested were killed " means that some of them protested and some of them didn't, and a portion of the people who protested were killed (for example, 50% didn't protest and lived, 30% protested and lived, and 20% protested and were killed.)

Those of you can be used when generalizing about a group of people. For example, "Those of you who feel this way." or "Those of you who think this." While some of them is usually referring to a more specific group of people. For example "Only some of you think this." or "Some of you feel this way."