It's not that "Revenue disallow" anything, unless you get an audit. The system is self assessment so you have to determine the business element of your expenses, and also the business use of capital assets.
I presume since you've distinguished that the above items are capital purchases, that the tax treatment is different to ordinary purchases - capital allowances (tax depreciation) rather than an expense. So if the asset is used 50% for business then you are allowed 50% of the capital allowance as a deduction.
Hope that makes sense!