The chances of getting two connecting studios are pretty high; very few of them don’t connect.
The best way to do a room request for DVC is through Member Services, but only the members can do that. So if you end up with two different owners that you are renting from, you would need to provide each of them with the other reservation number so they can include them in the request.
The TP fax can be used, just be aware some DVC resorts don’t look at them at all, others do at least some of the time. I have no idea if the Poly does. Ultimately it comes down to who is doing the room assignment and who trained them!
Do not ask for an upgrade, or even to change rooms. Any upgrade will “cost” extra points, which obviously you would have to pay for but could also wreck the plans of the owner. And capacity is 98%+, so there is little scope for changing rooms.
I assume you know about the lack of daily housekeeping. You can also use the free laundry using your magic band. Any dining plan needs to be booked by the owner, as does DME if you book it through DVC ; however you can also just book it direct with DME yourself.