I feel like the Malkavians need mechanical solutions for these problems.

On derangements: something like 'you go mad when it's a full moon' is vague. I feel like it'd be easier with a just any system, for example 'renew all Willpower during a full moon, but lose one each scene thereafter', which encourages the player to try just about anything during that night.

Twisting the mechanics also means the player doesn't lose agency by thinking 'oh well, time to act crazy I guess'.

On the combat problem: I feel like this is a symptom of a larger problem with the system. Combat has a system - it has levers everywhere which do things. Nothing else does, and you can't push buttons which aren't there.

I've solved the second problem by replacing Combat rules with general 'Contest' rules -- a single system for Extended and Resisted actions, which works for Investigations, competing companies, or snide remarks at Elysium...and sword fights, if you must.