Building a container for a loved ones remains is not a morbid project. Death is as much a part of life as birth....However, dealing with the passing of a loved one is a deeply personal experience, and depends on many things. Last fall, my mother passed away, without much warning, although she had been in declining health for some time. I learned then, from my father, that she wished to be cremated.
At the mortuary, my father, my wife and I discussed some of the requirements for the process to continue. We decided to build the container which would hold my mother's body for the cremation process, and also to make a container which would function as an urn, for the cremated remains.
For a number of reasons, we had several days to make, and then deliver, the large box, as it came to be called, and then several more days to complete the small box. I can tell you that having those projects to do, at that point on our experience, was a very valuable means of dealing with our emotions. Having my sisters there, and my father, helping to make decisions, helping to move stock through the machines, helping sand and pad shellac, gave us an opportunity to talk, cry, laugh, tell stories, and generally deal with telling our mother goodbye. It gave our hands something to do while we arranged travel, accomodations, services, took a few of the many telephone calls from special friends, and tried slowly to move forward. A really good thing for all concerned, under the circumstances.
Now regarding plans: One aspect of the design which may escape some discussion has to do with what is to eventually become of the cremated remains. In our case, when my father passes, and is cremated, both of the 'small boxes' will be taken out to the coast, and scattered in the Pacific Ocean. We do not desire to destroy either box in that process, so the design was to have the small box screwed shut, from underneath, with waxed and shellaced brass screws. Enough to preclude inadvertant opening, but not really industrial strength.
Since you have a little time, perhaps, consider the wood you will use. In our case, I built the small box for my mother from California Black Oak, which is native to the county in which she grew up. The inside bottom and top were lined with curly Claro walnut, harvested from the county from which her step-father's family had lived for several generations. The design was really simple, mechanically - a mitered oak box, with black walnut corner keys, and a book matched top and bottom. More coats of padded blone shellac than I counted. Clear wax, rubbed out with 0000 synthetic (white) steel wool.
What I'm saying is that you may have an opportunity to make the wood part of the story...
5 months later, I talk to my Dad almost every day. We work in my garage- shop-studio together almost every weekend, on some project or another. After their 55+ years together, I worry most about him being lonely. Oh, and I really enjoy the time with him, too. There won't be too many more years together on this side of the veil....
God bless you in your service to your father and mother and family.
Patriarch