The miles will be taken out pro-rata to the amount you each have, e.g. if you have 90k and Mrs sl1ppy has 10k, a debit of 50k would be taken split 45k/5k.

In theory you have no choice over this, but if their systems allow I imagine they might change it as you prefer over the phone - worth a try anyway.

Otherwise you can disband your HH account, but you'll have to wait six months to rebuild it.