Hi Pat, and welcome to MySwissAlps!
>> 1. Our first trip with our Swiss Travel Pass will be from Brig to Zermatt. Do we need to turn in our ticket and receive a plastic card?
No. If you have bought your Swiss Travel Pass online and printed it out on A4 paper, that is all you need. However, for any cable cars that are free with the Swiss Travel Pass, you have to present your Swiss Travel Pass at the cable car ticket office to receive a free card with a magnetic strip that can be read by the turnstile through which you pass before boarding the cable car.
>> 2. The schedule on SBB indicates a reservation is available for the above trip, but we are not able to secure one even though we have set up an account on www.swisspass.ch/auth/login. Please confirm that a reservation is not possible - either because of the specific train and route - or because we have a Swiss Travel Pass.
Without knowing your date of travel and time of departure, I can't tell whether a reservation is possible or not. If it is possible, it will be indicated in the timetable for that particular departure.
Reservations for travel within Switzerland are the exception rather than the rule - except for three of the panoramic trains, on which reservations are compulsory: Glacier Express, Bernina Express and Gotthard Panorama Express.
>> 3. We also would prefer a reservation when we travel from Interlaken West roundtrip that includes Lauterbrunnen, Kleine Scheidegg, Jungfraujoch returning through Grindelwald. Is it possible to secure a reservation for all or part of this adventure?
The only sector of that trip on which reservations are possible is the return trip between Kleine Scheidegg and the Jungfraujoch. I would not bother with reservations unless you are travelling in July or August.
If you have any further questions, please make sure to include your travel dates to ensure that any advice you receive is appropriate to the time of year you will be in Switzerland. For example, from late April to early June, and late October to early December many forms of mountain transport close for 4-6 weeks so that maintenance can be undertaken. The exact dates vary from place to place. Some mountain transport only operates in summer, and closes for around 6 months from October to May or June.