We will be doing buses so I’ll add it to HS day. Thanks!
Remember there are no buses directly to the parks from DS.
To get to DHS, you'll have to bus to a resort first and then get to the park via walking, boat, Skyliner or monorail. The only resorts that are walkable to DHS are BW, Yacht and Beach (or you can take a boat from any of those). Or you can take a bus to one of the Skyliner resorts, i.e. Riviera, CBR, Pop, AoA and then catch the Skyliner. Of those, CBR will be the easiest because the DHS Skyliner line leaves from the CBR hub, but you'll need to find out which CBR bus stop is closest to the Skyliner station.
Personally, I'd take a bus from DS to any one of the Epcot resorts (BW, Yacht or Beach, whichever came first; they might be sharing depending on what time of day it is) and walk to Epcot from there (it's closer than DHS). Beach Club is the closest with BW just a little farther, coming from the bus stops at each of those. That will be more direct and take the least amount of time via bus.
A final alternative is bus to Contemporary, then walk to MK.