What is the form I use or application process to remove an unreasonable executor?

Its not a personal thing but both executors are exceptionally useless and unreasonable in doing their duty, one of them could be classed as a vulnerable adult if I'm honest, the other is just uncaring about resolving this. 2 siblings are days away from being homeless and need the finances to renovate a really bad property they bought. One of these is one of the executor, the other executor has his own family and not part of this house reno and is very well off and couldn't care less. Every step of the process has been hardship to the point I want to chew my eyeballs rather than think about it. When these siblings are homeless this will fall to me to take care of.
It was a straight forward division of cash assets, no property and probate granted last October.

Is there a link or a form for me to apply to the High court to have one removed? I've searched courts.ie and see probate forms but none specifically in relation to this.

I don't think this is DIY job - you'll need to instruct a Solicitor to start proceedings.

However, there are other steps such as Revenue clearance that need to be completed before the estate is distributed. The fact that Probate is extracted would indicate that the exec (or their Solicitor) is doing their job; even if it isn't as fast as you might like.