Our family of four (8 & 13 yr old kids) are heading to Switzerland this June. Do I have to buy a Swiss Pass or Swiss Card for the adults in order to get the Swiss Family Card for the kids? Can I just purchase individual tickets for the adults instead?

I mainly want it for the trip up to Jungfraujoch. I believe our Eurail pass will provide the adults a 25% discount, so it's not really worth buying the Swiss Card for us. If we can still use a Swiss Family Pass for the kids, it's a no-brainer. Especially since the trip to the top is going to depend on the weather.