I have married a Hindu girl who was divorced with 1 son after she converted to Islam. My parents didn't know this and now they are trying to marry me to my cousin sister. Is it acceptable in Islam?
Technically it is halal to divorce a woman. But you must be aware that your reasons for this are very weak and the situation you describe is a situation where this "worst of halal" act could be a reason for this woman to leave Islam or lose her faith! I strongly recommend you to read surat al-Mumtahanah more exactly the verses (60:10-12). The verse says don't let a woman who just converted go back to her (former non-Muslim) husband, so Allah warns us that a new Muslim who was rejected by Muslims could easily fall back to kufr, shirk ... have this in mind!
If you however choose to divorce your wife which as it seems is the easiest way to stay safe from any discussion. I'm sorry to say you don't diserve this woman as a wife as a man should care for his family as our Messenger did and should be in charge for it (as stated in the Quran 4:34) instaed of leaving them at the first oppurtunity where he might get in trouble.
You should ask yourselfe whether you fear your family and instead of fearing Allah if you played in such a way with a woman? Don't you fear for your after life in just even thinking of divorce from a woman with a child just because your family didn't know?
You are a man you are allowed to get married to whom you want without the consent of your parents or family!
The best solution however is to speak things out with your family as proposed in my comment!
May Allah guide you!
No, this is never a valid excuse to divorce your wife. And your family can intimidate you only. They can't force you to marry someone else without your consent. Allah has clearly prohibited divorcing women who come to Muslims after accepting Islam. Allah says regarding this:
Sahih International: O you who have believed, when the believing women come to you as emigrants, examine them. Allah is most knowing as to their faith. And if you know them to be believers, then do not return them to the disbelievers; they are not lawful [wives] for them, nor are they lawful [husbands] for them. But give the disbelievers what they have spent. And there is no blame upon you if you marry them when you have given them their due compensation. And hold not to marriage bonds with disbelieving women, but ask for what you have spent and let them ask for what they have spent. That is the judgement of Allah ; He judges between you. And Allah is Knowing and Wise.