I would do it in Lightwave.

• export each figure to an obj keeping groups.
• load each to a seperate layer
• determine where the figures overlap
      - do a bucketload of selection and deletes to trim each geometry
      - another set of group selects and renames to get all parts unique
• weld up the joins
• then use phibuilder to set the hierarchy
  and create a figure in poser from phi file
   - adjust joint centers , and all the rest of the joint parameters
• if you remember to rename surface groups(materials) to be unique yer good on the texturing.

Thats a LOT of work if its not going to be a common use figure.