Here is advice from a Indian Sikh;
The whole situation with the Sikh woman supposedly wanting to marry a married Pakistani guy is very shady, especially Sikh women from India are very religious. Your cousins husband is not telling the full story.
The best way for your cousin is to contact the relatives of the "Sikh" woman, they will sort it out.
If your cousins husband goes to India, then there is good chance that he may go 'missing'. Honour killing is still pretty common in Indian Punjab.