That is bottles are countable while sugar is not. To make sugar countable, you need to add, phrases like a cube of sugar, 3 spoonfuls of sugar etc. Same as in Chinese, 一些糖, 二包糖,

小時候老師就說,有些東西是很難去量化的 (數不到的),所以英文來說不能當在眾數,如糖,米粒.等...雖然檸檬水不能量化....但你在檸檬水之加上一個能夠量化的器皿(Bottles) 所以 就能用上are,加上s 吧..... ..所以你也可以說成"two cubes of sugar" ......(大概是這樣吧)

There" are "two bottles of lemonade. = plural There" is "some sugar. = singular This is very basic.

what are you asking here ? if the sentence is correct ? :P to make it sound more natural you might wanna say : There are two bottles of lemonade with only a bit of sugar in them.