Your husband won't go hungry!
The week of your visit the staff from V&A will call you to confirm the spellings of your names and if there is a special reason for coming (birthday, anniversary etc). While they are talking to you, they will ask about any allergies. Tell them you would like to speak to the chef. They will arrange a time for you to speak to them.
Honstly, the nuts issue is very very easy for them to handle.
The "root" veggies, are normally a VERY small part of the dining experience, so they could easily switch them out for something else.
Hope you enjoy your dinner!