Hi, and thanks for posting your question.
The minibus company that gets the best reviews in Dublin is Dublin Minibus Hire
who are located 2 minutes from the Airport. They don't have an online booking but if you request a quote from the site they will ring you back and you can make your booking then. They offer 8 seaters to 24 seaters, so they should be able to look after you.
If this doesn't work out for you, here is a list of 4 other reputable minibus hire companies in the area.minibushire247 sixt executive travel solutionsminibus hire dublin
I hope this gets you sorted, however, if you have any difficulties, come back to me and I will give you details on some more.
Have a Great Day