Stability is the proper tool.
Think the issue is due the fact that you're trying to get volumes on non watertight objects. Capping the open boundaries might result in different volumes. I'm not sure about the way MM deals with open boundaries when calculating some volume ... so first of all close the open boundaries of your body using ANALYSIS/Inspector>AutoRepairAll.
Now you want to compare "nested" volumes. E.g body volume, arm volume and lower and upper arm volume.
On your source mesh (the body) SELECT the first level surfaces (e.g. the arms) totally. You might want to run Modify/SmoothBoundary on this selection. SmoothBoundary by default creates a face group for the selected faces. (Without smoothing the selection's boundary you might use Modify/CreateFaceGroup.) Do this for all the first level regions (arms and legs).
That done make a copy of the result (EDIT/Duplicate).
On this copied object select the second level regions ( lower arms and legs regions) and convert them to a face group as above.
That done make a copy of the result (EDIT/Duplicate) and select the hips as a third level and convert them to a face group as above
Now there are three object duplicates.
On each run EDIT/GenerateComplex. There, hovering over a face group boundary turns that line to orange. Click it to insert a parting surface. When you're done inserting all surfaces for the level Accept the tool. It will add another object flagged with "(complex)" in ObjectBrowser and green lines at the seams in the viewer. This object active do EDIT/SplitComplex to get watertight partial objects.
Calculate the volumes of the resulting objects via ANALYSIS/Stability.
