On the basis of what I think your sketches show, option C or D is probably most favorable. Treehouse design will generally be controlled by gravity (weight). Depending upon the internal forces accumulated in the members, member size and possibly even species will be important. In general however, the connections will be most critical for long-term strength of the treehouse. Forces acting through members eccentric (offset) to the connections will present more difficult strength considerations.
Connection eccentricity presents problems with the timber members as well as the connectors. Tear-out, bearing and grain cracking are some of the member connection limit states to consider. Determination of the forces acting on eccentrically loaded connectors and the transfer of these forces from the members is more complex than for concentric connections. For eccentric connections several forces can act simultaneously including withdrawal (tension), bi-axial flexure and of course shear. Therefore, it is desirable to keep connections as concentric to the connected parts as possible.
The diagonal braces in options A and B appear to have the most eccentric connections. Options C and D are more concentric to the tree and the timber members. The TAB bolts however are eccentrically loaded and will be required to resist shear, bending and possibly withdrawal forces. Your intuition is correct in that keeping these TAB bolts as short as possible is desirable. However, TAB bolts are proprietary products. As such they have a specified strength. This strength can vary depending upon the species of the tree. They are specifically manufactured for the construction of treehouses with the apparent purpose of reducing or eliminating eccentricity by acting as an artificial limb wherever you need one.
So, if you are able to determine the forces acting on the TAB bolt, it can simply be compared to the manufacturer specified strength. Use of these products has an added advantage in that companies that manufacture them often provide technical support at no charge.