It can be done but your looking at out of production equipment some of wich has a dark history associated with it. One is the 921 hd dvr, this is a receiver that I wouldnt wish on my worst enemy. What you can do is something like this.
HD tv 1 gets a 942 HD DVR dual tuner, the second tuner output is SD and the coax outputs in stereo, this can go to one of the SD tvs. Second HD tv gets an 811/411 non dvr single tv receiver. Second and third tv get a 625 dual tuner DVR that allows for individual viewing at both locations along with DVR being independant between both, last tv gets a 311 model receiver, doing this you will actually get DVR functions on 4 out of 6 of your tv's. Best bet is to get the 625 and 942 on the account right off the bat and then purchase the 811/411 and the 311 additional. There is a switch that you will need also called the dish pro plus 44 and the best way to get this without paying for it is to have dish network due the install themselves instead of having a sub or a dealer do it as they will have to charge to cover the cost of it. Explain to the csr when you call to order that your going to need this switch as your going to add additional equipment in, they can even sell you the two additional receivers when you set up your account. Make sure to get the CSR's operator ID and get all the details in writing and have them email you confirmation as well.