Is it safe to take my 10 mg flexeril at the same time that I take 25mg of zoloft (sertraline)?

Should be OK. There is no known interaction between the two medicines and so you should be ok. Also, 25mg of zoloft (sertraline) is a pretty small dose. But, some people may have reaction that is not expected and so if you experience any significant problem, consult doc. Good luck.
Most likely. Although there is a caution regarding combining medications with serotnergic effects, the risk of any such occurrence with the doses you indicate would be essentially nonexistent.