Am I obligated to notify my husband's children and ex-wife if he should die?

If your husband takes steps before his death to ensure that neither his house, his truck, or any other assets he owns become part of his probate estate, then that minimizes the chance for his children to be able to cause trouble. Unfortunately, if he is not willing or able to take these steps, then yes, you may have to deal with the children after his death. As for the ex-spouse, she wouldn't have legal standing with regard to his estate except for the fact that you say their divorce agreement requires her to receive his pension. That makes her a creditor. However, if he has named you the beneficiary of the pension in violation of the agreement, AND IF he takes steps to keep other assets out of his probate estate, she may have a very hard time actually being able to do much other than try to sue you personally for the pension. Your husband needs to make sure that he has a good estate plan in place, and that he's taken whatever steps he can to make sure it works as well as possible. If he doesn't, then yes, you may have to notify his children, and they will most likely notify his ex. If he does set up his estate plan correctly and gets good advice and good legal help, however, then you may not actually have to deal with the daughters after his death.