Due to the context, this may not seem relevant to Scrum but I have seen issues like this arise all the time in scrum teams in the industry.
The issue here is the lack of progress because certain members waste way too much time debating technology (this can apply to other aspects of the work too). Before I share my thoughts on this, a bit on semantics. I tend to use the word "impediment" for issues that arise externally, not within the team. So as Scrum Master, you would remove these external issues and protect the team from them. Nevertheless, this issue also falls within the scope of the SM; you must also protect the business by minimizing waste in the team.
Semantics aside, I think you can indirectly solve this problem by simply enforcing Scrum rules and ceremonies (sometimes it helps to follow things strictly to build that muscle memory; after a while, it will all make more sense). So to give a few examples of Scrum indirectly helping:
- Do you have all the business requirements written in your product backlog? In other words, someone must have spent time with store owners and come up with a list of prioritized backlog items? This someone is the Product Owner, who will have the final say about what should be built. Are these backlog items written as user stories?
- Once you have user stories ready for selection in the first sprint, you have 8 hours of the sprint planning meeting to kick off the sprint. Make sure the team understands the importance of these time-boxes and get them to stick to it.
- Ask the technical team members to come ready to the sprint planning meeting in terms of the technology stack as they would have roughly 4 hours (second half of the sprint planning meeting) to decide how they would deliver the selected user stories and they would even have create granular tasks representing the team's work for the next few days.
- You can also suggest a spike solution.
So although I get your point about this being a startup, but don't most startups have co-founders with defined roles?
So if you are the co-founder and responsible for operations, who is the co-founder and product visionary (the Product Owner)? No harm in these people doing some development too; doing a bit of role play is more productive than just arguing over technology.
At the end, the team may have to decide which co-founder will be the CTO and thus make all the final technology decisions.