penona, I'll happily to tell you all about how to access the literature, but just wanted to say first that so little is known about how early life influences later life that I don't believe you'll find your answers there. Firstly, a lot of it is just speculation, and secondly, as mumtoem says, it's a generalisation and can't be applied to everyone.
The fact (it does seem to be a fact) that little babies are very, very responsive to their mothers doesn't mean that they're easily harmed - you could argue the opposite actually.
You had an especially tough deal having DTs, but I can tell you that even just having one at a time is hard at best, and at times utterly knackering.
Maybe there're people out there who swanned about in a loved-up glow the whole time, but I've never met any! As far as I can see, we're all muddling through and often it's as much as you can do just to get through the day (or night) in one piece.
IMO if human babies were easily harmed by having exhausted parents, then the human race would have ended long ago.
I think the fact that you're reflecting in an honest way on what it was like, and using that experience to change what you do, puts you streets ahead of most of us.
Now to answer your questions: A good way to access the medical literature is to use a search engine like PubMed. [http://www.ncbi.nlm.nih.gov/sites/entrez This] should get you to the PubMed home page (if not, you can google it). Then you type in search terms - cortisol crying turns up lots of papers for example.
The problem is that without a sub, you can't read most of the papers in full, only the abstracts (summaries). That means it can be hard to tell the good studies from the bad ones.
My impression of the literature on this topic (from a fairly superficial read) is as I mentioned above, that babies are responding very strongly to cues from their mothers. But it's nearly impossible to measure the long term effects of parenting, so the literature isn't helpful there.
I think it's fairly clear to experts that babies in extreme situations (ie abandoned babies in orphanages) can grow up to have attachment problems. However there's nothing remotely proven about how the behaviour of an ordinary, knackered mother impacts on a baby long term - and I'm sure you can see that having a knackered mother who is there as you grow up is a completely different kettle of fish from a mother who disappears one day and never comes back. You can't extrapolate from one to the other.
So IMO the possibility has been raised that what we do could affect our children in later life, but nothiing is proven.