Off peak, return next day train ticket query

lea

Hello

I'm trying to find the cheapest way to do the following this weekend:

Fri 24th July: 2 adult off peak train tickets from Royston, Herts to London Kings Cross, then tube tickets to North Greenwich, then back to Euston area.

Sat 25th July: 1 adult returning from Euston to Kings Cross, then back to Royston, Herts. 2nd adult travelling to Kings Cross, then needing zone 1 and 2 access for day, until travelling back to Royston in the evening.

I can't seem to get my head round how to get the best value for money tickets!

Single tickets from Royston to Kings Cross on the Friday evening are £20.80 each. To add a travel card on would be £12, but I believe paying by contactless for zones 1-2 has a cap of under £7 which may be the better option, meaning a total of £28 each for the Friday only. On Saturday, all day travel cards going from Royston to London are £20.50. Should I mix and match?!
There is also an option of off peak anytime return ticket for £32.30 each, not including underground travel.
Can anyone give me any pointers which would be best? Have been looking at this all night and I cant fathom it!

Thanks so much
Lea

The_ICT_Engineer

There's a 'Overnighter' ticket from Royston to London for only £18.50 which can be brought on the day,

http://www.thameslinkrailway.com/tickets-and-fares/overnighter/