MN1 for Children Born Outside of UK

Hi
I want some advice on applying for my children MN1 please. Here are my circumstances:

1. Got my ILR April, 2018 based on Tier 2 PBS 5 years. Couldn't apply for family (wife and two daughters) since they had joined me in UK about a year and 3 months later.
2. Son born in UK in 2015. Filed for his MN1 based on my ILR in 02/2019. Still waiting for decision.
3. Applied wife and two daughter's Tier 2 PBS Extension (was expiring at end of March, 2019) earlier this month. Have appointment with Sopra Steria tomorrow for Biometric etc.
4. Family would complete 5 years in UK in June, 2019.

Questions are:

1. What's the best way to get to naturalisation with minimal cost for the family?
2. Provided the family gets Tier 2 PBS extension, I was thinking of filing for ILR for wife only when she completes her 5 years in June. However I was thinking of filing MN1 directly for my two daughters after my wife gets ILR under 'Discretionary Leave' without having to go through ILR for them. Is it advised or risk rejection?

Appreciate any help thanks in advance!

Children born abroad are expected to hold ILR and should apply when your wife does.

Children born abroad can apply for British citizen once they hold ILR and either parent is also apply for citizenship and the other also holds ILR.

Thanks much CR001, have a further question please: what if I apply for BC next month since I'd be eligible for one and later when registering children under MN1, one parent would be BC and other ILR?