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!
Good luck!