Thank you for your hints. Also, for anyone in this situation, using cloudflare has no effect.Hi Stefan
You should first keep the hosting unique for each domain.and try backlinking to each domain from different sources by trying different long tails (we cant change the main KWs as all websites targeting same KWs).
This should work and impact on results as soon as you do the above things. I can assist you better If I am able to know your sites.
I have seen cloudflare effects the ranking. You can also buy the ranking service.Thank you for your hints. Also, for anyone in this situation, using cloudflare has no effect.