By your description, the receivers you want on the whole home are on the same dish (HR22 and H23 connected to a Slimline 3).
The Slimline 3 would need to be converted to a SWM (or, yes, you could swap it over to the SL5.. with the right splitters... green label SWM Splitters), Both the HR22 and the H23 would need DECA's (One each), and the D12 will need a Bandstop filter.
The DECA's allow the receivers to communicate over the coaxial network, The Bandstop Filter stops the Coaxial Network traffic from interfering with the satellite signal on the D12, and the SWM allows the Coaxial network to run.
Once you have The Whole Home Service Activated on the account, the receivers on the other dish will show it, but it wont work, unless it gets changed to a SWM also, with DECA's and what not, and then would only share among receiver connected to that dish.
For ALL the HD receivers to share using Whole Home, they would all need to be on the same SWM network (just one dish).