No problem
UV mapping is a beast to get your head around! One rule of thumb to go by is that if EA mapped it that way, it's good to go. There's really not much need for re-mapping per se in this case. You'll just need to rearrange the map a bit to fit everything in. Below are the steps I'd take for the whole project. I know you've already done a lot of things, but following these steps this may make mapping it easier. Here goes:
1. Export from S4S/Open in Blender the Modern Colonial double bed HLOD .blend and delete the entire mattress.
2. Choose
File - Export - Wavefront (.obj) and export the Colonial bedframe mesh as mesh object.
3. Export from S4S/Open in Blender the Seaside Single bed HLOD .blend and delete the entire frame.
4. Import the .obj you created of the Colonial bedframe mesh. (
File - Import - Wavefront (.obj) and navigate to your saved .obj of the bed frame)
5. Select the frame and click
tab to make sure you're in Edit mode.
6. Click
1 to activate front Ortho view of the mesh. Make sure "Limit selection to visible" is turned OFF.
7. Use border select (
b) to click/drag and select all of the vertices on the left side of the bed frame mesh. Then drag them toward the center using the red arrow handle until they fit with the left side of the mattress. Then unselect these vertices.
8. Use border select (
b) to click/drag and select all of the vertices on the right side of the bed frame mesh. Then drag them toward the center using the red arrow handle until they fit with the right side of the mattress. Then unselect these vertices.
9. In edit mode, click "a" to select the entire bedframe mesh. Then in the UV editor window, click "g" to grab the map, and move the entire bedframe UV map off of the mapping square.
9. Back in the main mesh window, activate the "Object Data" window. Make sure the UV map of the mattress mesh group and the bedframe mesh group are both named "UVMap." If they don't have identical names for the UV map, you'll lose the map of one of the mesh group when you join them.
10.
Tab into Object mode. Right click on the bedframe mesh then
shift+right click the mattress mesh to select both of the mesh groups. Then click
ctrl+j to join the mattress and frame into one group.
11. Use
b (border select) or
c (circle select) to select all of the bedframe in the UV editor window. Once it's all selected, click
s/.75/enter to resize it to 3/4 the original map size. Then it's like a puzzle to move the uv map bits around the map square until they all fit.
Below is the combined map I ended up with (no new "unwrapping" required - I just resized the bed frame UV map and moved the bits around to fit):
Hope this helps! Let me know if you have any more questions :D (it was late when I wrote this so probable that I missed a step somewhere)