As all moms here would probably say, it's great that we have such concerned husbands/fathers like you! Good on you, your wife and your kids!
Personally i believe, folic acid is your best bet. I think taking Chinese medicine/herbs/tonics wouldn't be ideal, as it might mix with whatever your wife's gynae is giving her. Chinese and english medicine/herbs/tonic, cannot anyhow mix.
I guess if i have a no.2, i would want my husband to help out with the household chores and no.1, so that i can get more rest. Maybe a prenatal massage from time to time as well?
Good luck on your wife's pregnancy!