Disclaimer: I'm not a lawyer, and this is not qualified legal advice.
Johnny, first off, if you're seriously considering this, then go see a good lawyer. And be sure to consult with a lawyer who specializes in business and/or immaterial property laws; and not, for example, a divorce lawyer.
Before seeing a lawyer, you should read up on the basics so that you can be more efficient when meeting the lawyer, and you'll require fewer (expensive) billable hours. Here is a mini-overview of the different types of immaterial property laws to get you started.
You're not stealing their idea; and even if you where, ideas cannot generally be protected legally. If anything, you're building a company that might be at risk for a trademark dispute, and could potentially lose the right to do business under its name.
If you go ahead -- and just to be clear, that might very well be both possible and smart -- then be sure to get the trademark on the name. Trademark it both in Ireland and in the EU while you're at it. Having the trademark is not a 100% guarantee against future problems, because trademarks can be revoked under certain circumstances, but it is the "legal high ground" if it comes to court proceedings.
My advice would be:
- If you can get the trademark, proceeding may be an option. Consider the alternatives, and discuss your exposure with your lawyer, but it is doable if you want to.
- If you can't get the trademark, then absolutely don't do it.
One last thing -- have you thought about contacting those other guys, and maybe do a joint-venture with them instead.