Welcome.
We are a family (2 adults, 2 children (8+11).
You will undoubtedly save money with a
Family & Friends Railcard, which will give you 1/3 off fares so long as you're travelling after 10:00 (this time restriction is only for the South East).
Could you let us know what times you plan to travel? I will for now assume that you'll be travelling "off peak".
I found out that this could be a Boundering Zone 6 ticket in combination with a Travelcard 1-6.
The combination of fares you've been suggested is (adult/child fares):
Off Peak Day Return Reading-Boundary Zone 6
Route: Via Slough - £10.50/£5.25 (railcard £6.95/£2.00)
Off Peak Day Travelcard Zones 1-6 £8.50/3.20 (railcard: £5.60/£2.00).
Alternatively, you can purchase a Reading-Zones 1-6 Travelcard which is both combined into one ticket. This is slightly more expensive (£14.35/£4.15 with railcard).
There are two routes from Reading to London: one line goes to London Paddington and is served by fast, frequent trains taking ~25 minutes; the other goes to Waterloo and has trains every 30 minutes and takes around 1h30 to Waterloo. The line from Waterloo goes through various places which may be of interest such as Richmond, so it can be useful if you happen to be near one of these stations.
Note that the combined travelcard from Reading is valid on either route; to use the boundary zone ticket on a train from Waterloo to Reading you would need to pay an excess fare to a
Route: Via Ascot ticket, which is around £1 each.
Unless you don't plan to use public transport to get around London, I'd not recommend using an Oyster card for this trip - a paper Travelcard will be better value.
Would this be possible and where could we buy these tickets?
The boundary zone tickets + travelcard combination needs to be booked at a ticket office or via telephone - it can't be done online or at a ticket machine. The combined travelcard can be bought from a ticket machine or online as well.
There's no advantage in buying these tickets in advance.