Putting the bone in boiling water for a few minutes simply "cooks" the marrow, and that helps remove the stink until it drys enough to be pulled, or scraped out of the bone. When the bone comes out of the water and cools down enough to be touched, cover the bone with a good oil to keep it from drying too much, while you wait for the marrow to dry and shrink. If you put the bone in sunlight, the marrow should dry within a day or two, and then removing the marrow should be easier. There is connective tissue in there, and you may have to dip the bone into boiling water, again, to soften and remove all that tissue.
If you are worried about the strength of the bone, as a handle, you are being astute.
The bone will get more brittle with age, no matter what you put on the outside. However, if you fill the space in the bone with epoxy before inserting the tang, the epoxy will lend a lot of strength to the bone handle, and keep it from moving in relation to the tang as it ages.
That won't protect the bone from chipping off it the knife is dropped on rocks, or concrete, or banged against something solid, but it will help harden the bone for ordinary usage as a handle.
If you are going to use cross pins to hold the bone to the tang, you have to drill the tang holes, and the holes through the bone handle BEFORE you apply the epoxy and glue the bone to the steel tang. The cross pins have to be cut oversize, and tested, and be standing by to insert after the tang is placed into the bone cavity.
Epoxy does squeeze out the pin holes, but can be wiped off with a rag . Put wax on the outside of the bone, so that any unwanted epoxy does not adhere to the bone where it will be seen. Wax is a release agent.
Have fun with your project. Some bone handles are truly elegant. A couple of our knife makers here have produced blades with Jawbones as handles.