It has been suggested, by Dr Richard Bernstein in his book 'Dr Bernstein's Diabetic Revolution', that Vitamin C above about 400mg per day will increase blood glucose levels. I don't know whether he's right, but someone else may. Check how much Vit C you're getting between your Vit C and the multivitamin.
The others shouldn't do any harm to bg, as far as I know. If you're eating lots of fresh veg you should get most of what you need in your diet, but you're not likely to OD on a small amount of supplement. I supplement in winter. My bg levels have been a little lower since I stopped my 1000mg slow-release Vit C, but I don't know whether that was because I stopped them, or because of the low-carb + metformin improving things anyway!
I took Berocca tablets at one point which is supposedly very low in sugar and it made my levels go up quite a lot. It confused me quite a bit so I contacted them and they said it shouldn't effect sugar levels as it hardly has any sugar. Confused, I simply stopped taking them...
I take a cod liver oil off the spoon everyday but don't take a multivitamin or vitamin c, provided you eat a good range of fresh fruit and vegetables there really isn't any need to take vitamin c or a multivitamin.