I've been a developer off and on for 16 years. I have also been a team lead, a CTO and a CEO. This is a very common issue and like most common issues contains a counter-intuitive solution.
I'm assuming that reason you are asking the question, to begin with, is that you suspect these two developers are not working fast enough.
Primarily this comes down to trust. You mentioned that you were not an IT guy. That begs the question as to how you were able to hire these two developers in the first place?
Perhaps you had an IT consultant hire them for you? If you hired them yourself then you do in fact have something to be concerned about.
What I know about developers is that it takes a good developer to hire other good developers. Hiring developers without knowing anything about development is a recipe for bad outcomes.
See, the thing is if you know beyond any doubt that these two developers were qualified to do the job when you hired them and you are paying them a salary commensurate with that skill then you have nothing to worry about in general.
Using whatever project management strategy whether it be SCRUM/Agile or whatever is not going to make a bad developer better nor will it make a good developer even better.
If you are not sure that you hired the best people for the job then the best thing to do is to find out ASAP by hiring a consultant to come in and evaluate the situation.
This need not be a huge undertaking and shouldn't require a lot of money. The consultant can look at the project history and give the developers a few skills exams to see where they are at on the knowledge scale of the codebase you are working with.
If the consultant comes back with bad news then you should have the same consultant help you screen new applicants to replace either one or both developers. Yes, you will lose time by doing this up front but you will save even more time over the long run.
If you hire 2 new developers who have been vetted by a person who knows how to tell a good developer from a bad one then you will have nothing to worry about and you can trust that what they are doing in terms of speed is appropriate.
If these 2 developers you have are in fact up to the task then ask yourself are they getting paid what they are worth? Under paying a developer is also a recipe for bad outcomes.
Whatever you thought you were saving in hourly fees or salary is going to come out of lost time because the developers are not motivated to help you succeed.
After all, what's in it for them? If they have no equity in the company then they know they are just hired guns and can be let go at any time and have no real stake in what you are trying to accomplish.
It very well could be that they are underperforming but that is either because they are not experienced or skilled enough for the task or they do not feel valued by you and have no real incentive to bring their A-game.
Another important point to realize is that developers are constantly being beat-up by unrealistic requirements from the marketing/admin side of the house.
If you are not a developer that 10% of what is viewable on a screen is the tip of another 90% in code that is making it happen and that interacts with many other moving parts in the code.
What appears to be a simple new feature request or change to a layman is in fact not a quick thing at all. If you have hired a good developer you can trust that they will be honest about the time it takes to implement and in that case you must lower your expectations to fit with the reality of the situation.
It all comes back to making sure you start with a good developer and for that, you certainly need someone who knows how to tell the difference between good and not good.