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)

                Dad

________|___________

|                                         |

DAD                            Dad

|                                         |

DAD                               Dad

|                                           |

MOM                                Dad

|                                           |

MY FRIEND              Her boyfriend