I am just down the road from you in Canonsburg, PA. If you like, give me a call some evening this week or you and your husband can stop by the shop I work with in Washington, PA on any Thursday evening.
You can mix and match certs from different agencies.
What you do also need to realize is that even though, as far as operators are concerned, an OW card is an OW card, the courses are by no means the same. There are different standards for each one and the instructor you take the class with will make a huge difference.
Standards are generally the minimum ones they have to meet and you have to meet to be issued a card. At that, there are shops and instructors that may not meet the minimums but will still issue a card to you as long as your credit card or check clears.
There are also shops and instructors that go way beyond the minimums to ensure that you are safe, skilled, educated, and comfortable in the water even if it takes extra time. The shop I am with is the only one in the area with an onsite indoor heated pool specifically for scuba training so I'm not limited by having to wait for a minimum number of students, I can often work with your schedule, and if you need more time in the pool or classroom, there is no extra charge.
If the shop does not have its own pool, it's likely that you have very limited choices on class times, smaller classes may require extra cost because the shop has to rent a pool for that, and you may be doing classroom at one location and driving a fair distance to another for the pool.
I also agree that mixing certs may be a good thing if you choose the courses and instructors carefully. For the above reasons. Advanced through shop XXX may be woefully less or much better than shop YYY.
If you'd like more info my number is 724-255-3765 and I'm available most evenings after 3:30 PM.
Feel free to give me a call.