Marriage in cousins : legal or illegal ?

My friend is in a relationship with a guy who is his cousin and they want to marry each other. There relationship is as follows: GIRL'S >MOM'S>DAD'S>DAD'S>DAD(SAME)

BOY'S>DAD'S>DAD'S>DAD'S>DAD(SAME)

they are third cousins.

               Dad

________|___________

|                                             |

DAD                                    Dad

|                                              |

DAD                                    Dad

|                                              |

MOM                                 Dad

|                                             |

MY FRIEND                      Her boyfriend

is it legal for them to get married?

both of them have different surnames and are jain by religion ?