I actually think these figures are wildly too low, I have not doubts a surviving Reich would have a TFR well over 3 perhaps even closer to 4 for the greater part of the 20th century. They did not merely offer heavy incentives for getting married and producing children, but they entered the psyche of the German volk, just like religious communities, made it a holy duty to create a family, raised it as the ideal.
"The Amish population has increased from roughly 5,000 at the turn of the 20th century, to a quarter-million today, a pace of growth likely to continue."
-City Lab
This is a fifty-fold increase over 110 years, roughly 4 generations. These people, have the chance to return to modern civilization, with all its liberal values and luxurious amenities, but they for the most part(I recall it is usually 2/3 to 90%, depending on the community) decide to stay living in an outdated lifestyle, in the Amish community. Why? They were socialized in it, internalized it's values, and social momentum. All this, with relatively free access to a completely different lifestyle and world view.
Nazi Germany, is not only less free as to what outside information, but they controlled the education system. Nazi German teaching has both the fetishization of freeholding and sanctification of procreation, alongside the relative poverty of the cities, with near free land to serve as a lure. We tend to think of a decline in birth rates as inevitable, because we take our western values and emphasis on individualism, and the glorification of self-fulfillment, as self evidencing fact, and thus the net financial negative of children in a
REGULATED industrial society forever depresses birthrates. But if you remove one of the core pillars of liberalism, the equality of people, from the set of implicit virtues as Nazi's did, you end up with a system, were people refusing to have children are harming not just themselves, but betraying everyone around them, their people, and the society which raised them, by giving their proportional "birthright" of the earth's population, to every other race, country, and peoples. I think the pressure to have a pair of children, is inescapable in such a value framework, that even without policies that encouraged creating children, the birthrate would never fall below replacement level, moreover fecundity would necessarily be a focus of both national and personal pride.
Also keep in mind, your birthrates come in the context of 5 decades of occupation and de-nazification, disillusioned with what destroyed their fatherland, particularly in the more agrarian communist occupied east.
https://www.jstor.org/stable/2768366
is a source I found useful. You might find it helpful for your timelines.