is cousin marriage illegal in india ?

Me and my cousin are third generations cousin n we want to marry. We belong to south India.Basically v r from mangalore(Karnataka).though our parents don't approve of our relationship n decision but still they r standing by our side for sake of our happiness.They say that our customs n traditions doesn't allow this.Our aunts n uncles are totally against it.They say that it is also illegal to marry your third cousin.My dads mothers mother and her dads mothers mother Were real sisters. And so my dads mother and her dads mother become first that case my dad n her dad become second as per d family tree I suppose we r third my question to you is will I b able to register my marriage in d court of law? Is it really illegal to marry my third cousin as per Indian Law?will i have any legal issues?I have read d Hindu Marriage Act but wasn't able to understand the word "Sapinda".Now do we fall under the SAPINDA category?N am I right when I say we are third cousins?Will our marriage come under Special Marriage act or Hindu marriage act?