Hi there!
I may be able to answer questions, because I take a beta blocker, Zoloft, AND Xanax! I sound like a junkie
My whole panic/anxiety thing started as feeling my heart race/thud all the time. I was put on a cardiac event monitor for 30 days and had a couple rough episodes, one of which convinced me to walk myself to the ER. My monitor actually caught something legitimate but harmless. After this, I had a stress test and echocardiogram at a cardiologists (both came out fine). I was put on a beta blocker,
Metoprolol, 25mg twice a day. With the beta blocker, my heart rate is usually around 70 (was 90+ before). What they do is block the effect of adrenaline on your heart. After seeing an electrophysiologist, I finally found out I have an electrical misfire in the upper chambers of my heart that can cause it to randomly race. I also feel flutters in my chest pretty frequently, which I know are harmless, but I hate.
After all this, my heart problems went away but anxiety remained. Lightheadedness, disconnectedness, feelings of panic and fear, sweating, trembling, nausea...it was pretty awful. I went to se my doc and was put on Zoloft and Xanax to help while the Zoloft kicked in. I was prescribed Xanax at 3x a day as needed and am now down to about 1 a day (I break my .25 in half sometimes). I am still on 25mg zoloft and have been for about six weeks. I tried to go up to 50mg but my body was not having it (I had only been on Zoloft for a week at that time). I was feeling GREAT for awhile, but now my anxiety is creeping back unfortunately, and I am going to try for the increase to 50mg and see what happens. My doc is pretty much the perfect "Xanax Doctor"

...she requires me to get in touch with her EVERY time I run out and tell her how I am feeling. She will refill as long as I am not abusing it and it is helping me function.
SO, to make a long story short (if it isn't too late for that), YES you can take Zoloft, Xanax, AND beta blockers. Beta blockers are not habit forming...the only thing you need to remember about them is they can not be abruptly stopped because that can cause major problems with your heart. It is not harmful to take Xanax in moderation and only when you need it and you should get a doctor that does what needs to be done for you to feel better. Good luck with Zoloft as well...it is kind of nasty to get through at the beginning, but for the brief time I had where it kicked in I felt wonderful. Sorry for the long-winded answer