His family want him to marry a girl who is not religious and they say that she will change in time

The Prophet (peace and blessings of Allaah be upon him) commanded the one who wants to get married to look for a religious woman. He (peace and blessings of Allaah be upon him) said:  “A woman may be married for four things: her wealth, her lineage, her beauty or her religious commitment. Look for the one who is religious, may your hands be rubbed with dust (i.e., may you prosper).” 

A wife is a life-long companion, and she will take care of his household and all his affairs. She will be the one to bring up and teach his children. Religious commitment is the thing that makes a woman chaste and keeps her away from bad things. So you must choose a wife from among those women who are religiously-committed and fear Allaah. 

What I think you should do is to strive to influence her and make da’wah to her through your family or some of your mahrams so that she will improve and adhere to the straight path. If she adheres to the straight path and improves, then marry her. 

Otherwise, I think that you should look for someone else, for you have no guarantee that you will be able to influence her; she may not respond, or you may be influenced by her, for no matter how much faith and taqwa (piety) a person may have, he is still human and is still subject to change or influence.