Firstly, I want to say that what you're doing is quite generous and truly admirable. Regarding nutrition, I would say that your best bet would be to really focus on eating organ meats frequently (as I stated before, it's my belief that a few mouthfuls eaten frequently is probably a better way to extract the greatest % of nutrients from it). You would also want to focus on eating a lot of pastured egg yolks, given that they are great sources of cholesterol and essential fatty acids that these babies need for brain development. I eat 4 a day myself that are hard-boiled so that there is as little degradation as possible. You should probably drink a lot of mineral water to replace the calcium and magnesium that are being leached out of your bones. The K2 from the organs and egg yolks will aid in remineralization.
This is a case where I'd actually be hesitant to recommend supplements because though the mineral content of breast milk is tightly regulated and not necessarily influenced day-to-day by diet, therapeutic doses of vitamins or minerals outside of the bounds of our evolutionary history may actually be dangerous for these kids. Now, when you stop breast feeding eventually, you'll be less restricted and can more aggressively replete those minerals. The generally accepted post-natal vitamins are probably fine though. I think it might be safer to get vitamin D from the sun for as long as possible and then supplement with small amounts (500-1000iu) spread out over the course of the day just in case.
Cod liver oil shouldn't be necessary if you're eating enough pastured egg yolks, but if you were able to find a DHA supplement that is tested for heavy metals and so on, that may be a worthwhile thing to consume.
This is a case where I'd say that you'd want to be eating a lot of grass-fed animal fat and of course I would say you shouldn't really dip below 200g of carbohydrates.
Regarding oysters, unless you can be certain that you've sourced them from pristine waters (on another planet?) I would avoid them. I'm a lot more conservative about these sorts of things when we're talking about an infant.