You can check availability for 4 tickets, even if you don't have the miles. If there are 4 tickets in CW redemption available, you should be able to book and upgrade 4 WT+ tickets.
Put yourself and wife into a household account, then you can share the miles. Put the kids in too so that you can spend the miles on tickets for them as well (and so that you can collect the miles they earn).
Kids tickets seem a little bit cheaper in WT+ for some reason in my experience.