Hi Teresa,
Just to clarify, is the business structured as a partnership and not as a limited company?
For partnerships, tax is payable on the partnership profits. This is defined as sales income less expenses (not including the partners wages). So they are not taxed on the €300 per week. They are taxed on the partnership profits (if any). Has the business been making any profits?
If the business is set up as a limited company, the two business partners will pay tax on the actual wages they receive from the company i.e the €300 per week.
The amount of tax that each person pays depends on their tax credits. If for example, a person's only tax credit was the "single person tax credit" which is worth €1,830, they could earn €9,150 before becoming liable to income tax. However they would still be liable to pay the minimum PRSI payment for self employed persons which is €253 p.a.