Parental Leave is not the same as part-time work and cannot be counted as time off for the purpose of redundancy calculation. If you take of a case of someone who took 14 weeks straight Parental Leave 2 years ago, their redundancy payment will not be reduced. This is also true of someone taking days off for Parental Leave currently.
Fom the Parental Leave Act, 1998
14.—(1) An employee shall, while on parental leave, be regarded for all purposes relating to his or her employment (other than his or her right to remuneration or superannuation benefits or any obligation to pay contributions in or in respect of the employment) as still working in the employment and none of his or her other rights relating to the employment shall be affected by the leave.
It is true that you employer can make one postponement of Parental Leave, for a period of no greater than 6 months; however the employer will need to set out why and how this will have an adverse affect on the running of the business. If they cannot do this they have to give the leave. Based on what the OP has outlined, if the company is looking at redundancies, they obviously have not got the work or costs are an issue. Parental Leave reduces employer costs and reduces manpower requirements. I can't see how they could refuse.
Anyhow, based on the above, Parental Leave would be my recommendation.