Hiya, I'm incredibly impressed with your presence of mind, turning your Dad's question back at him. I've just had a little boy and my 2.2 yr old girl is still feeding. While Mum never actually said outright "you should stop feeding her", I found no matter what issue came up - sleep, feeding, behaviour etc - her response would ALWAYS include a suggestion that it might be time to stop feeding DD. Very irritating - just had to learn to grit my teeth!
In terms of support, I was lucky that on my peer support course I met someone who'd tandem fed and somehow that 'proved' to me it was possible in a way that no thread or book could. Irrational, I know. That said, I've found Adventures in Tandem Nursing really helpful. There are loads of personal anecdotes in there, including the question of pain during pregnancy.
It seems to be worse for some people than others and at different stages of the pregnancy. For me it was OK to start with, then got really bad late in month 5. Probably not relevant at this time of year but I found it was worse if I was cold - so it can sometimes be exacerbated by external things that only trial and error will identify.
Apparently supply does drop but if they still want to nurse, they're probably getting something from it. Might explain why DD started waking in the night again to feed around this time. Colostrum replaces milk around month 4 or 5 I think - certainly in my case if I managed to squeeze anything out it was more like a clear gel than anything you'd recognise as milk.
I asked DD the other day if she preferred my milk now DS is here or before, while he was in mummy's tummy. Now! she said firmly - but there was no question she always wanted to feed while I was pregnant, particularly in the last 3 weeks when I was off on maternity leave. She shifted from feeding morning, post work and night to feeding about 8 times a day. In the first week or so that DS was back home (I stayed in hospital for 2 nights until we'd got our act together) she kept up that rate and would also ask to feed whenever she felt a bit insecure but would usually only want a minute or so. Think it was mainly about asserting her right to milk. Thankfully, she seems to be dropping back to the old 3x a day pattern now (DS is 6 weeks old).
As the book points out, there's good and bad things about tandem feeding but for me, it's been great to have one area of mothering two where you don't feel torn about whose interests come first: even Mum has had to concede that seeing the two of them feeding together is a lovely sight. And having a highly efficient 'breastpump' certainly made the engorged stage much easier to handle this time round!
Very best of luck on your own "adventures" .