Hello khl
Yes, it is okay to purchase one Swiss Half Fare Card to retrieve the Swiss Family Card.
However, only the person that holds the Swiss Half Fare Card is entitled to purchase half fare tickets; the other person must purchase full fare tickets; you cannot share one Swiss Half Fare Card among multiple people.
If you only want the Swiss Family Card, without the Swiss Half Fare Card, you could purchase the Junior Card at the counter (not online), for as little as CHF 30, valid one year.
Working as a ticket inspector, I often meet tourists on the train using tickets while there would have been a better offer, being more beneficial or more economic.
To help you choosing a pass or tickets, you would have to disclose your travel plans here. There might be better offers than those you have in mind.
Furthermore, I suggest to first finish the itinerary planning, and to look at the tickets options as the very last step in your planning. Often, people wish to change plans but are tied to a specific ticket offer that they purchased as a first action, yet that then kills the freedom of changing plans at short notice.
Kind regards,
Roland