二 is not a simplification of 兩. You can think of 二 as numeral 2 and 兩 = couple. English "2" can mean both the numeral and the quantification. So "I have 2 apples" is equivalent to "I have a couple of apples". However, there are certain situations in Chinese that 二 can be used as a quantifier as 兩. These sort of situations are found only in poetry or classical Chinese. For example, 二人世界 which means, "a world for two" in the context of two lovers being together as if they are the only two in the world.

二：used in car number ,phone number ,room number ....；Tuesday:星期二；February 二月 两：used in talking quantity . 两个，两天，两个月 so, 二is number , 两is quantity .

二就是一个数字 两除了做数字还可以做代词和形容词

Actually they are the same:D But critically, “二” is usually used in writtrn language, which, “两”, can be used in both situations. E.g: You can write “I have 两个 apples" or "I have 二个 apples". But when speaking, most native speakers may say “I have 两个 apples". Also you can just replace them with number "2". It's still common. Am I clear? Should you have any questions, just feel free to ask me. ^ ^