Thanks for providing photos. You have a couple options to choose from.
The size of gaps between your four front teeth is too large to restore with veneers. You will most likely be looking at oversized teeth if restored without braces. The best option is to get braces or Invisalign treatment to close those gaps prior to any cosmetic treatment for smaller teeth. Once the gaps are closed, then a cosmetic dentist can do the composite build-up/veneers to bring those smaller teeth to the correct size, shape and contours. Composite veneers, if done well; will be the most conservative approach to treat this.
Another option is to get porcelain veneers for those two side teeth after braces.
Please work with good Cosmetic dentist who will also work with an orthodontist to resolve the problem. Hope this helps. Good Luck!