Stating the relationship (and not just "cousin": it is a vague term) should be enough (e.g. it is the son of the brother of your father? [add names]).
But why you cousin want to sponsor you (and not me)? This is a question embassy want to know. They want to be sure you will comply with the visa (not working and returning within the visa timeframe). In Europe it is not frequent that a cousin will sponsor so much. Or are you paying your travel, and you the accommodation (and ev. food)? You should write it clearly. Note: he should not just have enough money to sponsor you, but also that such trip will not effect significantly his finances.
Too much documents seems to be seen as a bad sign (but I read this about US, where in person interview are preferred, and ev. they ask you for further documentation). Check the important documents.
From your history, you ask related visa question every month. I hope you are trying to get the perfect application. If you had few rejections, stop applying for the trip this September: every time you will get less and less possibilities (and it is suspicious).