Your is a possessive pronoun which refers to belonging to a person or people that the speaker is addressing...

Their is a personal pronoun which refers to belonging to or associated with a person or people whereas...

'Two' refers to number, 'Too' refers to also or additional whereas 'To' is a preposition indicating direction.Example1....

‘Less’ denote quantity where as ‘fewer’ denote number.For example :1. No less than fifty students...

‘UNLESS’ expresses a condition, It is always used in the negative sense. Thus ‘NOT’ is neverused...