Q1: It is correct to say either, "their English is at a beginner level" or "their English is at a beginner's level" because "beginner" is an adjective describing the level, while "beginner's" is showing ownership of who speaks at that level. I have heard both. Q2: Either question is correct, because sugar could be uncountable (as in, a bowl or large bag of sugar), and therefore you should use "how much?" But, sugar becomes countable when you put it into packets. So then "How many sugars?" really means "How many packets of sugar?" but people don't want to say all that so they just say "sugars." So, the answer "two sugars" is correct and it means "two packets of sugar." I hope I helped! :)