You have a number of options, but the simplest is using glue - a strong 2-part epoxy.
If you can drill/scrape out a hole in your handle material that you can slip the tang into, you won't have to use two slabs with the tang inlet half way into both halves. But you can also do that. A good epoxy will be more than strong enough to hold the tang in the handle - without any pins. But you can drill and pin if you wish.
And epoxy will fill up any gaps or voids in and around your tang in your handle. If you have a large gap, mixing in a little of the sawdust from your handle will help blend it in with the rest of the handle.
Don't be afraid to use more than enough epoxy. It's pretty easy to clean off the excess, but you can have problems trying to add more in to fill any gaps/voids.
Some knife makers just use pins to attach the handle, but you have to have a pretty close fit. Some just use epoxy, where a good fit is best but the epoxy helps "smooth" things out. And many makers use both - they glue the handle on, and then drill/pin it after the epoxy has set.
So you have a number of choices. It all depends upon what you want to end up with.
Just my humble thoughts to share. Take them as such.
Mike Ameling