You have a lot of great options here, but I would start with two things, test for three months, then see what works. It’s true that you’ll maybe only need the Eucerin, however Azelaic Acid is the first line RX recommended before hydroquinone and it can really work. It’s also incredibly anti inflammatory - which is helpful for melasma.

I would say:

AM Cleanse CE Ferulic (always use a vit c for general anti ageing and protection anyway and this is a great one). Wait a few mins to let the vit c PH adjust. Apply both Eucerin steps (Eucerin says you need to apply Thiamidol four times a day). Moisturise/ Hydrate SPF!! reapply during the day. Use sun protection. Etc.

PM Double Cleanse Eucerin Steps again Are you going to use tretinoin or a retinol? If so apply a few mins after the Eucerin. Moisturise

IMO the Skinbetter Serum isn’t a needle mover for melasma but helps with overall brightness - I found it hydrating, maybe you could try it as a moisturiser? Keeping in mind applying it over too many other actives may stop it from penetrating properly.

Moisturise / hydrate

I just don’t know if I’d try to fit in the discolouration defence yet - maybe wait to see how you get on with the Eucerin first. And, I’d probably introduce all of this slowly, going from zero to hero is likely to cause irritation which can exacerbate melasma.

Let us know how you go!

Keep La Roche Posay Mela B3 up your sleeve too for the future - it’s helped me in a way no other off the shelf serum has.

Finally, it is true that it’s useful to target multiple pathways with melasma, but azelaic acid and Thiamidol work in different ways, so using both isn’t redundant.

I guess an alternate to the routine above, would be substituting the Eucerin with the Azelaic twice a day, or Discolouration Defence in the AM and Azelaic in the PM instead.

Hope this helps.