You mean same age, different source (and genetics) but included in the 35 chick count?
Do you have another coop, or what's your plan? That's too crowded even just for night time.. I know because I have done it too!
At 5 weeks old the mum should be thinking about teaching her young to roost and maybe booting them to curb so she can get back to business. Are both broody's raising both sets of chicks or are they real staggered and not sets at all? I know we all have different situation that can arise so I'm just trying to get a clear picture. No judgement, just a discussion.
Don't believe everything you read. What you're seeing isn't anywhere near cannibalism. And white laced red Cornish might not be the same as Cornish cross (beasts) or what have you. ANY chicken, I don't care what breed goes ballistic for the rich taste of blood. The make happy peeps which alerts their friends to join in the party. Most often I would describe it as an accident gone bad.. they won't just eat another chicken.
Since you aren't seeing any wounds or bleeding it could be over preening, as suggested by another poster feather picking to each other, boredom etc.. check after dark with a flash light for parasites running away on the broody hens to get your clearest picture of what's truly going on there and JUST be sure that isn't the issue, despite not seeing red angry skin.
The 18% starter you're getting probably does have the added amino acids and vitamins needed. I looked up the guaranteed analysis on the UK for chicks you are using.. I would skip it personally looks to me like despite having higher protein it may be lower in amino acids. and it's pricey, mixing your current feed with turkey or game bird starter crumble might give you more bang for your buck, which feed store are available to you?..
https://foragecakes.com/portfolio-items/farmers-helper-babycake-ultrakibble-for-chicks/
Guaranteed Analysis:
Crude Protein (min)……….. 29.64%
Lysine (min)……………………. 0.43%
Methionine (min)…………… ..0.32%
Crude Fat (min)……………… 10.67%
Crude Fiber (max)……………. 7.30%
Calcium (min)………………….. 1.35%
Calcium (max)………………….. 1.85%
Phosphorus (min)…………….. 0.54%