Revenue have been making a lot of errors recently. Somewhere along the way your uncle & aunt appear to be taxed as individuals. You should contact the tax office or email them. See
Here and click on contact locator
Tell them that your uncle & aunt are normally assessed jointly (Any unused SRCOP and or tax credits can be used by the other)
Your uncle should get an increased SRCOP to 42,000 for 2006. All his income will then be taxed @ 20%
In respect of his tax credits he appears to be only claiming the marriage credit of 3,160 and PAYE credit of 1,270
What about the other credits that can be claimed
Are they paying rent?
If I were you I would also check out previous years. You can go back 4 years.
My understanding is that unemployment benefit is taxable with the exception of the first 6 weeks as mentioned in a previous post. Maybe it is not taxable
Ask revenue when emailing them
If it is there will be no additional liability to income tax - see previous post
I calculate the situation for 2005 as follows
Taxable Income:
33765.61
Charged as follows:
33765.61 @ 20% 6753.12
Tax Due: 6753.12
Less T/Credits: 4430.00
Taxes Deducted:
2323.12
Tax Due Nil