you basically need to lyse ALL cells present, then get rid of lipids and proteins. This will leave you with DNA+RNA.
I have done extraction of nucleic acids from blood. It isn’t hard, but you need a protocol. I will try to look through my papers and see if i find it.
Do you also need to isolate the DNA from the RNA? I have also done that, and it is not hard either.
Just a few pointers: if you are going to use whole blood, the yield surely is going to be fairly low, since most of the blood is red blood cells, and they do not even have a nucleus to provide you nucleic acids 🙂
However, if the blood samples you have do not contain any kind of cryoprservant, most of the cells will get lysed anyway during thawing, and in the end you lyse them anyway to get your hands to the nucleic acids. A bit late to say now, but separating white blood cells prior to freezing and using them greatly increases the yield and quality of the process.
Of course, if the whole point is that you have to use frozen whole blood, then just forget about what I just said and pick some straightforward protocol from the manufacturer of your choice 😛