I have looked at the 2 websites and I cannot see how anyone could be confused that one was the same as the other.
I can’t see that clauses 2 or 3 are actionable.
Just because they may be next to each other when someone does a Google search doesn’t mean there is confusion. It may be that your Optimisation is simply better than theirs and gets higher rankings. Clearly, that has niggled them.
Certainly, with regard to item number four, you are not allowed to publish images showing the clients logo.
If you are based in London and they are in Dublin, would need to apply to court in England to get an injunction to prevent you from trading and carrying on with these activities.
Depends how much money they have the risk going to court and how much money you want to risk defending any action.
My suggestion would be to make halfway house proposal whereby you remove any goods from the site which you do not sell and you remove the image of the fighter referred to at 4.
Then, see whether they come back to you saying that you have not gone far enough.
If you want me to word the letter for you, please let me know and I will submit a Premium Services Proposal for you for which there is an extra cost. All you would need to do then is to cut and paste the words into your own letter and send it off.