What are steps. My boyfriend is Illegal and we have been dating for 4 years and I'm in love with him and his family. Is there any possible way to help him and his sister become legal us citizens?

There is nothing you can do for the sister- in fact, there is nothing your boyfriend can do for his sister either.

If you get married you can petition for his legal status, however since he is illegal, he would need to go to his country of origin for his interview and waiver hearing. You would need to file a I-601 waiver to waive his illegal entry into the U.S. and give him legal status. However, there is a high burden of proof on your part and simply by leaving the US, he would be subject to a 10 year entry bar if the 601 waiver is rejected. So its a gamble. Even if he does gain legal status, there is nothing he can do for his sister.

NOTE: i assumed "illegal" to mean illegal entry into the US. If he had legal entry, but his visa expired, then it WOULD be possible to make your husband legal without leaving the US- the sister would still be out of luck though.