Candidly, it may be difficult to accomplish anything here, at least, absent any compelling evidence against the husband.
If she had not yet been buried, the family could request an autopsy. With an autopsy, it could be determine if anything unusual was in her system. As the burial has already occurred, the family would need to have the body exhumed. For what is probably an obvious reason, bodies are rarely exhumed.
To pursue anything here, there would need to be something suggesting culpability on the part of the husband. For example, evidence of drugging the wife, evidence of physical abuse or a neighbor overhearing them arguing before her death. Absent something such as that, I don't see much likelihood of success here.
I regret that my answer is unfavorable, but please understand that it would be unfair to you (and unprofessional of me) to provide you with anything less than a truthful response.
Also, several customers have asked how they may direct a question to me in particular. If you specifically want me to assist you in your legal matter, just put "FOR JOSEPH" in the subject line and I will gladly pick up the question as soon as I am on-line.