As for the fares, YMMV of course, but hopefully you'll find something. It depends a lot on when you fly and how much flexibility you have. You are looking during the heavily-traveled spring break time, but bargains are likely if you fly on off-peak times - I see that your window starts on a Friday and ends on a Sunday - probably not the best days for cheap flights. I'd start looking at flights now, if you see good prices, go ahead and buy. But say for example, Delta is only showing K and higher fares but when you look at the seat maps, they are wide open, I'd hold off and see if Delta sells some LUT fares as the dates get closer.

And yes, you could use PWM for one ticket and the companion cert for the other one. Remember that PWM means that the passenger earns no miles or MQMs, and the companion ticket is not supposed to get miles or MQMs, although people (including me) have reported getting miles and MQMs for these tickets. So if you are buying 3 tix, and you personally want to earn miles, and don't care as much if your companions don't, buy your ticket as the regular ticket for the companion cert, and the other tickets as the companion ticket and the PWM ticket. Also, you'll have to find LUT fares in order to use the companion cert at all.

Just did a couple of quick searches on delta.com, and I strongly recommend that you skip trying to fly out of PSC and use SEA or PDX instead. You'll likely have to double-connect (SLC and ATL) in at least one direction if you fly from PSC, and the fares will be much higher.

Found tickets for PDX-TPA for $367.39 per ticket leaving Saturday March 21 (red eye only), returning Thursday, April 2, but the return is in K class, so you couldn't use the companion cert. This ticket is a T fare on the way out. Also, Delta is selling the one-way PDX-TPA as a T fare for $127.20 all in. If you wanted to lock in this fare now, you could buy the tickets as one-ways and just hope that you are able to find decent prices on the return as well. You could use PWM at $100 per ticket, and pay only $81.60 total for all 3 passengers for the outbound portion of your journey. Doing this would make it impossible to use your companion certs, as I think they have to be used for a round trip. Also, PWM isn't a very good deal in general (lots of threads about that on FT), but it really depends on how much you value your miles for real award tickets vs. just saving some money now.

As the travel dates draw nearer, in my experience delta will lower their ticket price on flights where they still have lots of seats to sell. However, given that this is spring break time, these planes might fill up, so you are rolling the dice.

Delta has a reasonably convenient "flexible travel days" search option that will help you a lot in your search.