family tax credit - this is the standard tax credit that used to be called Family Support. It's available to everyone whose income is below the threshold (which varies depending on how many kids you have)
in-work tax credit - an extra top-up which is only available to families [who are eligible for family tax credit] who work 30+ hours per week. Generally speaking it is not available for beneficiaries.
minimum family tax credit - don't even look at this, it's for if your family earns less than $20K (or something like that) in a year.
parental tax credit - an alternative to maternity leave payments when your baby is born. Maternity leave is generally always better $$ but the PTC is available to people [who are not beneficiaries but] who are not eligible for maternity leave - such as if you are on a fixed term employment contract.
Our family situation is such that we have three kids at home with my DH as SAHD while I work. We get a tidy sum from IRD each week (family tax credit and in-work payment) and we are also eligible for accomodation supplement from WINZ (which is based on your income and your house expenses etc rates, insurance and mortgage/rent and an online calculator is
here.
Our mortgage is probably of medium size for anywhere except Auckland; we have a pretty sunny house so that keeps our power bill down (to an extent); we run two vehicles; we operate on a strictly cash-only basis so that debts don't get ahead of us, and we make sure that we put some $ into our savings account every payday so we have something to fall back on.
Umm it's hard to know how to answer but if you want anything else, go ahead and PM me