I don't know anyone who intended to tandem fed and then weaned the toddler once the newborn actually arrived.
I know women who intended to but never got there due to issues during pregnancy (aversion, milk drying up etc). Some of those actually weaned the toddler in pregnancy but then found they could feed them again once baby born and free flowing milk.
But stopping tandem feeding once there are two children because of latching issues? Not heard of it. Not saying it doesn't happen just that it's something I've not heard of.
Would be interesting to know if there's been a study done, I doubt it though.