Just with regards to tandem feeding, the Natural Nurturing Network (UK)
had a tandem feeding theme to a newsletter once, years ago.
This is completely un-controlled as far as a proper study goes, but it certainly appeared that, the further the two siblings were apart in age, the more likely/bigger the aversion issue was.
IE, the closer the siblings were in age, the less aversion mothers experienced to breastfeeding whilst pregnant then subsequently tandem feeding.
~ Birth/Earth Activist, Lactivist & Mother/Baby Intactivist ~