Hi Kitty - not meaning to weigh in on a conversation which is already done with but reference the IMM0008 and 5406...
I completed the IMM0008 with only my details. I am the PR app and only have common law partner who is Canadian and therefore is not included in this form.
On the IMM5406 I included me, my Canadian partner, my mother, father, all siblings (including step and half - and I have loads but don't know where they all are now, nevertheless). We were very confused with this as the guide isn't 100% clear - so I called CIC and was told to fill in as above. The person I spoke to stated that if I failed to mention anyone on the IMM5406 it would mean that I could not (if found to be eligible) sponsor them at a later date.
If this was not correct I have royally screwed up.