Tarek,
the quad is formed by the 8 non-overlapping cells of the Windoku corners region and the Girandola region.
These cells are r5c1289 and r1289c5. Because we need 2 sets of the same 4 digits, r5c1289 must contain 4 different digits in these cells and r1289c5 must also contain these 4 digits. Furthermore, these digits are paired, so r5c19 = r28c5 and r5c28 = r19c5.
The other quads are in r5c3467 and r3467c5. Both contain the same 4 digits. Because r5c46 can see r46c5, these are also paired, so r5c46 = r37c5 and r5c37 = r46c5.
Here is the solution for your G1 with the first quads in green and the others in blue.
971|423|685
835|976|241
246|851|379
312|748|596
769|315|428
584|692|137
197|534|862
623|189|754
458|267|913
In SudoCue, I use the following names for the Windoku regions:
- LT Pane, RT Pane, LB Pane, RB Pane
- Left Stiles (r159c234)
- Right Stiles (r159c678)
- Top Stiles (r234c159)
- Bottom Stiles (r678c159)
- Corners (r159c159)
Finally, unless I made a serious mistake, your last puzzle has 5 solutions.
Ruud