I must be doing something wrong, I can't play as either of these heroes. Right now, all I can do is blame riot for the nerfs on kayle and poor stats/other stuff for Sivir. Pls help me with item builds, skill builds, or other complaints against these heroes.

Sivir is a pusher, play her like one. Max Q first, W second. When you get E depends on how many casters/disablers the enemy has.
There are many items you can get for her. I prefer Philosopher's Stone, Berserker's Greaves, Bloodthirster, Infinity Edge and Stark's Fervor. You could also get Phantom Dancer, Black Cleaver, etc. Lately I've been toying with Guinsoo's Rageblade as well, but I haven't got a good matchup to test it yet.

Early game keep W disabled, and conserve your mana for Q. It can do a ton of damage if it hits the enemy twice, so try to aim it well. Try to pressure the enemy off the lane, and then take down the tower at level 6 with your ultimate.
Your job for most of the game is just to push down enemy towers. You can help out in team battles with your ultimate, but try not to get into a direct fight.

Sivir is different...

Its almost like Sivir is playing a different game. She's a pusher/farmer/supporter. And she does an amazing job at that. Basically, Sivir can just ignore champions and focus on lane pushing, and really win games by doing that.

I play Sivir like she's a personal asset to the team. I get Philosopher's Stone, Berserker's Greavers, Stark's Fervor, Aegis of the Legion, and Warmog's to abuse her ability to wipe out full waves in under 5 seconds. When you choose her, try not to gank with your skills. Pretty much if you are in a team fight use your ult and try to damage as much with your Q spell but your most important aspect is your amazing pushing power.

Kayle is more of a support tank now, still getting used to his new change.

tbh, I don't know how you're having trouble playing Sivir. She takes out waves of creeps easily with her Ricochet skill, barely using any MP in the process. On top of that, she has her Q skill which has a very long range and very good damage if both hits connect. In my opinion, she has to be one of if not the best laners in the game.

With sivir, due to her attack speed, I feel getting malady helps the team out a bit.

Thx for the advice got Sivir, I guess I wanted to play her as a hero killer, which isn't possible I guess.

I still need help with kayle, as far as items and skills are concerned.

Kayle

Runes: Mana regen page

Mastery: Put 9 into offense (get the 15% magic pen mastery), and I put the other 21 into utility.

Items:
1. Meki Pendant
2. Socer Boots
3. Meji Soulstealer
4. Zonya
5. Rod of ages

Skill:
q,w,q,w,q,r,q.....then its up to you

bascially what you do is spam you q and heal up with w. Its helpful to get last hits with the q skill on champions cus of your meji.

*** You really need a full man regen page in order to be efficient in spamming Q

This is my personal set-up, im sure others have theirs that work also.