I'm sorry for your loss and wish you and your family strength during this difficult time.

With regards to your question, it really depends on what your goals are. If you invested the $12mil in a relatively conservative portfolio and withdrew only 3-4% each year ($360k+ per year), you would be able to at the very least maintain the principal.

You seem to enjoy a relatively comfortable lifestyle right now so I'm not sure this necessarily changes everything for you. You may have more room for discretionary spending. Or you may choose to maintain a similar lifestyle and use the money elsewhere. You and your family could donate more thank $100k to charity each year with relative ease.

I would strongly suggest to be careful about lifestyle creep. You hear stories in the news all the time about lottery winners and pro-athletes who lost all of their millions because they were not sound financial planners. The amount of capital your father passed on to you has the capacity to serve you and your future heirs well into the future if managed properly.