What I understood from your post:
- You want to print only six pages in a booklet form to a target Tabloid size paper
- 2 pages are inserts (pages 3&4)
Please try this:
1. File > Print Booklet > click Print Settings > select Setup tab
2. Select Paper Size > Tabloid and select Orientation > Landscape (the second button)
3. Click OK to go back to the Print Booklet dialog
4. Select Range and type > 1-2,3-4 (i.e, all the pages except center insert)
5. Click on Preview and confirm if the page sequences are correct (6,1, and reverse 2,5)
6. Print this lot and then print the insert pages separately on Letter size paper