He probably can. First, it's not a given that there is necessarily a conflict of interest in his representing your husand, based on the prior relationship; but more importantly, only the *client* can bring up a conflict of interest. It's not the other party's concern whether there is a client. In this case, you are the other party, your husband is the client, so he's the one who would raised an conflict issues.That said, IF the ex-brother-in-law had done legal work for you and had, as a result, gotten information from you as his client, in that case, he might not be able to represent your husband, since an attorney is not supposed to use a former client's information against that client at a later time.