I'm Doug, and I'm very sorry to hear of your family's situation. My goal is to provide you with excellent service today.
I can answer your question for you without the need for you to access the social security site.
To begin with, each person is only entitled to collect one social security benefit at a time. I presume that your mother is presently collecting either a spouse benefit or a retirement benefit based on her own lifetime earnings.
When your father passes away, she will be eligible for a survivor benefit, if it is greater than the benefit she presently receives.
Under social security law, your mother's survivor benefit will be equal to 100% of the monthly benefit that your father is collecting at the time of his death----and I am sure that she must know what that amount it.
When he passes, she will need to go to social security with a copy of their marriage license, a copy of his death certificate as well as both of their social security numbers, and social security will assist her in apply for her survivor benefit.
You may reply back to me using the Reply link and I will be happy to continue to assist you until I am able to address your concerns, to your satisfaction.
I hope that I have been able to fully answer your question. Please be so kind as to rate my service to you. That is the only way I am credited for assisting you.
I wish you and yours the best in 2016,