good question
jmo.....in the case of IDCC
most should look at the USPTO issued patent as the underlying patent for an invention (where they usually file first). That patent.....and it's specific international equivalent(s)...could be considered your immediate "family". When you add in US patent continuations/continuations in part (and their international equivalents) to the initial priority (initial invention)...you have...let's call it an extended family.
A "portfolio"..... would typically be a group of patents or patent families (continuations, continuations in part, and their associated international equivalents) that are grouped together around a particular technology or solution....not so much just a particular "invention"
jmo