It seems like your main problem is the mobility champs that bamf into your face and do high damage (Yi, Le Blanc, Katarina, etc) In those instances, two things will save your bacon as Morgana. 1. Save your stun for when they come in. No need to try spamming it for harass, that's what your pool is for (that, and farming/denying farm.) 2. Wait for it, be prepared for it, anticipate it. Easier said than done, but knowing they're going to do that be ready to use your stun instantly. Once they're in, you've got to splat it right in their face before they can hit you any more. Pool, walk away a little and AA (or walk away a lot if you need to be safer.) Keeping behind your minion wave will help for some of those champs as they're less likely to pop in if their escape route is a bit harder. And remember that Black shield.........it's a life saver against AP guys, but don't waste the mana against Yi (since he already used Alpha Strike to get in range in the first place.) For team fights, look for two opportunities.........if their tanks comes crashing in, stun him, drop a pool and watch the ensuing carnage as your buddies splat him, or, even better, if you can pop the stun on their carry you can turn the tide of the whole battle. Proper placement will depend on the situation, but generally, stay at least two to three Morgana sized gaps behind your tanks, Black Shield them so they can go in and initiate (or Black Shield yourself if you're going to Flash in, ult, and Zhonya's.) Don't move into the fray in team fights if you're not tanky enough and Black Shielded, let the melees and tanks do that. Hang back and stun targets of opportunity, shield your squishies if they're jumped on (melee or tanks if not,) and layer the ground with generous amounts of ichor. Going in for your ult is so tempting, but you HAVE to wait for the chaos to ensue or you'll get focused down quick. Once the fun has really started, people lose track of everything since they get focused on killing that one particular target they're hitting (or they simply can't sort everything out from the jumble.) THAT is when you walk up and ult........their attention has been disrupted, their reactions are slowed, and your shield has probably reset, so you can put it on yourself as a safeguard.
And Morgana can build glass cannon, tanky, or a mix. Everyone and their brother seems to have "the" Morgana build, but you can build her effectively any which way, you just have to change your play style accordingly. I, personally, like a bit of ap/life item combos (Rylais, RoA,) Sorc boots, some defense (Zhonyas is what I love the best, combined with Abyssal, but you can put in a Banshee's Veil if they have a single stun,) and then just more AP items, depending on the situation.
I'm horrible at Syndra, so I can't help there lol
For Sona in team fights, poke from afar, heal your buddies from afar, drop that speed boost to engage or disengage. The ONLY time Sona should be anywhere near the ruckus is when she is flashing in to ult. I stress, FLASHING in to ult. Don't walk up, someone will splat you quick. Practice it in bots, it takes some skill to maneuver your flash and aim your ult (just ask XiaoWeiXiao lol) but you can lock up a group of champs and turn the tide of battle if you get it right. Mostly, though, Sona is easy........stay as far behind your team as your Q allows and spam both it and your heal. And avoid choke points, if you can, unless your ult is still up, since someone will trap you there and kill you. If you ult is up, feel free to lead the entire enemy team in there if they're chasing you and do a turn around flash ult to ruin their day (provided you have backup.)
Best of luck on the Rift!
