Isn't Lister an Orphan?

I have pieced this together before.
Obviously Red Dwarf is not huge on continuity, but it makes sense if you think about the timeline this way:
Lister was found under the pool table by a couple whose names we don't know (or maybe their names are mentioned in Ouroboros but I forget). Let's call them Bob and Sue. They raised him and he considered them his parents.
When Lister was 6 years old, Bob died, and then Sue remarried (let's call her new husband "Charlie") and Dave considered Charlie to be his stepfather (as mentioned in Marooned).
At some point after that, for circumstances that are unclear, Sue and Charlie were no longer able to raise Dave, and left him with his grandmother (either Sue or Charlie's mother). Or possibly he went to live with Sue's mother while Sue dealt with Bob's death, and then when Sue remarried they took him back into their lives. Or something.

(If you want to see my entire "dissertation" on Lister's family line (with a few more crazy theories), you can look at my blog post here: http://blog.tornsignpost.com/2012/10/red-dwarf-x-fathers-and-suns-and-whimsy.html )

To give another example of the fluid internal history of Red Dwarf - In "Thanks for the Memory" Lister copies the memory of an old girlfriend and gives it to Rimmer. When Rimmer finds out he realizes why some things didn't make sense, including why he had his appendix removed for a second time.

It also means Rimmer had his appendix removed whilst fairly young and then, with 8 months of Listers memory inserted, remembers Listers appendicitis whilst going out with the girl.

In "Legion" the titular character removes Listers appendix (again), saying it was about to turn septic.

We can either explain it as fluid writing or (my favorite) with all the time and dimension jumping over the years, it's no wonder the crew's personal history is confused.