Hi,
This link has more through information about the subject.
http://www.inis.gov.ie/en/INIS/Family%2 ... cument.pdf
On page 51, you can see this paragraph :
Given the level of risk, which cannot be fully mitigated by undertakings
of financial support by family members, the financial thresholds for
earnings to support an elderly dependent relative must be high enough
to meet the foreseeable expense. Therefore a sponsor of an elderly
dependent relative will be required to have earned in Ireland each of
the 3 years preceding the application an income after tax and
deductions of not less than €60K in the case of one parent and €75k
where 2 parents are involved. Where the elderly dependent relative
has a guaranteed income into the future this can be used to partially
offset the financial limits (bearing in mind however that a person with a
sufficient personal income for their needs cannot reasonably be
regarded as financially dependent).
For your questions,
1) €60000 is a must but even that income does not guarantee a successful outcome.
2) There is only one sponsor for one relative. Therefore, the income requirement is only for one sponsor, you cannot combine your salary with your spouse to reach that amount. Also, as it is written above, this amount is an after tax amount and you need to have this income for 3 years before becoming eligible to apply.
There are other considerations, too. I think you should first read the document in the above link.