As you know, the .256 Newton is a good round, but it has long since faded from common usage and reloading data is going to be hard to find. The .30 Newton is even rarer.
Reloading is not particularly difficult, nor is it at all dangerous if done properly. From what you are saying, all you are going to need are bullets, primers and propellant to get going.
ABCs will give you a general idea of what reloading is all about, general hints and techniques, etc. Read that before doing anything else. Normally I would agree with the suggestion to get a reloading manual or two on top of that, but they would be most unlikely to provide loads for either of those, so my personal call would be not to initially.
I fully agree with the earlier suggestion to look for a notebook or log in your father's effects - the 'recipes' he used himself. If you can find that, you're on your way. There might also be labels on his ammo boxes - they may look cryptic but can tell you what loads he was using. Moreover, every rifle has its own preferences and normally a reloader has to go through a trial-and-error testing phase to determine what his rifle likes best; in your case, your father will have already done that.
Whatever you do, follow the recipes exactly at first. Don't try to substitute one powder for another or a different weight of bullet.
I would also suggest that you start off using your father's reloading gear - the stuff won't have deteriorated sitting on the shelf. If something isn't working or is a real pain to use, then consider upgrading or replacing it.
Where are you located? I'm sure we can find somebody to walk you through it initially.