King size bunk bed are designed with the ability to split into single beds, this is not a common practice when building full-size bunk beds. If you choose to do that, you need to drill holes in the bottom of the corner posts in the top bunk and tops the corner posts in the bottom bunk. You will then inserting the plugs into the holes to hold the beds together. These holes must be adjusted carefully and, because of the size and weight involved, you will want to use dowels that are at least 3/4 inch in diameter.
As with a regular bed, king size bunk bed needs guardrails on the top bunk. This prevents the rolling out of bed, and the rails must extend at least five or six inches above the mattress to be effective. It also needed a rugged ladder. Steps need a robust support point to the top bunk, so it will not wobble or otherwise move while in use. While steps can be made from wood, “hooks” bent metal is usually the best way to attach it to the side rails.
If you want your king size bunk bed as a single unit, the assembly not be a problem. Corner posts will be high single posts, and both beds will attach them. This results in the most stable piece of furniture; you just need to ensure that services are thick enough to support the extra weight.