Evelyn: Depends; a Lichbane Eve gets most of her damage for Lichbane (physical damage as it increases your next normal attack) after using a ravage (magical damage). Damage wise, Eve is a true hybrid. Stack both types of armor against her is the only effective way.
Twitch: Spray and Pray is physical damage, the bang (expunge i think its called) is magical. Havent seen an AP Twitch ever though, dont worry about the magical part. Your best defense from S&P is walking around. He shoots in lines, making him miss atleast half his attacks. An recently unstealthed/S&P-ing Twitched cant be outdamaged, hes got a massive attack speed (180% from these abilities alone). Dont try, avoid it.
Physical Damage - damage from autoattacks. Characters with high/dangerous physical damage include Ashe, Tristana, Master Yi, and Jax.
Magical Damage - Damage from spells and abilities. In addition to obvious casters like Veigar or Ryze, other less expected sources may include tanks like Amumu or assassins like Evelynn.
For most of the part, this is correct. There are a few exceptions like Pirate's Parley (physical damage) or Corki's Passive (magical damage). All these abilities clearly state it though.
My tips for tanks fight Eve or Twitch: Armor and dodge mitigate most of thier damage (Eve will remain to her her initial spike because of ravage, which is magical). Oracle Potions or wards work better though. If you jump on them before they jump on you, theyre useless.