Hello,
yes they are generally safe, unless there is a specific reason your doctor tells you to not consume those nutrients (magnesium, vit C, ashwaghanda, etc). Generally, vitamin C is very beneficial during pregnancy was it helps strengthen immunity which generally is reduced during pregnancy and it also helps absorb iron.
As far as the amount of vit C, it varies person to person. I always recommend following bottle dosage when in doubt. I cannot make specific dosage recommendations without you being a client of mine unfortunately.