Which is more appropriate: giving money to the parents to perform 'Umrah, knowing that the couple have not performed 'Umrah or Hajj before, or keeping the money to perform the obligatory Hajj for the couple next year, or should all four (the couple and the parents) perform 'Umrah together?

If the spouses are able to perform 'Umrah, they must do so immediately; because it is obligatory once in a lifetime. There is no sin upon the husband if he gives some money to his parents for them to perform 'Umrah with it before the time of the obligation to strive for Hajj, and this is not considered a dereliction of ability. So, when the ability is found at the time people set out for Hajj, striving immediately becomes obligatory, otherwise, there is no sin. Therefore, if the time for Hajj comes and you both have sufficient means, hasten to it, otherwise, there is no sin upon you.