Hello Pioyiegriez98
Another possibility is to obtain a refund of the HFC of one parent and to buy a new one with the children. If you bought the HFC with a SBB account, it should be possible to initiate yourself an automatic refund before the first day of validity without handling fee. Other resellers may also offer this possibility.
Refunds via SBB Contact Center are also possible with a handling fee of 10 CHF.
Kind regards
Danhiel