Best use of miles ,help please

I know this is a subject that some of you like to get your teeth into by I just can't get my head round it so all help welcome!
The situation is this.
Originally I was going to take my eldest two to NY in aug but have decided to go end of may instead,working on the assumption that g fares will be available and I will have approx 100,000 miles to use and don't mind using tem all up what will be the most cost effective way to achieve at least UC one way with PE the other or UC both ways
Thanks in advance
Blacky
The situation is this.
Originally I was going to take my eldest two to NY in aug but have decided to go end of may instead,working on the assumption that g fares will be available and I will have approx 100,000 miles to use and don't mind using tem all up what will be the most cost effective way to achieve at least UC one way with PE the other or UC both ways
Thanks in advance
Blacky