my main partner is a good yoshi mainer, and the egg is stopped by fireball tornado gets smacked away easily given yoshis momentum and bad timing on either of your parts. He has a very nice low lag air game that can punish you and when he gets you high in the air the knockback on the Uair tailwhip sends you vertically at low %'s. Be very careful of yoshi's second jump super armor, it will mess you up because when you try to move where the combo would continue you can lose position and get % racked up on you fast and maybe die when you had them on the ropes. So how do you stop Yoshi? short hop approaching doesn't work you will be at 30% damage by those exploding eggs he tosses, they hit you even if you air dodge most the time, this is one of the times rolling in is a great approach, if he goes to the egg roll then you stop fire ball and after that he has stopping lag you can run up they most likely try and *** or F-smash roll under and Fire punch death. Your up b may be the only effective way to send yoshis heavy *** vertically, unless he has high % and bad DI don't try to send him off the top to often, if you do it should be by 2 way, Fsmash with up angle or UpB superpunch. the best way to kill yoshi is stay by the edge and use your shield grab to get him off then WoP with your Bair or * my prefrence because i am so used to facing a yoshi mainer, stay forward, run off Fair back flip to stage run off and repeat when he wastes his second jump wait for him to start falling, don't let him touch any platform then keep him low down and WoP your Bair. If you have a lot of practice you can get quick easy kills off of shield grabbing bthrow and then Dair spike but my best friend who mains yoshi has seen this 1,000 times so he air dodges it every time so now i say the best method vs a good yoshi is Fair untill they need to use the double jump wait for them to lose Armor then Bair WoP for a prat fall or a horizontal KO
Peach has crap for an approach but the turnip dash, floating into a wigi is death in my book. If they float to you jump past them underneath so they can't hit you with a Dair and then Bair them to the side of the stage you started, from here i Tornado in get her up and do your best % building combo and push her to the edge and try and force her off the stage and Bair+edge guard. If she approaches with the turnip then fire ball spam her, either WoFB or just reg spam the fireball depending on their variation of the turnip dash, they generally just sprint in throw it and go into a lagless combo that has you at 60% and falling off your side right off the bat, but to avoid the turnip and they'll still be in a sprint, roll under and then start a dash and you can use the running fist to hit them as they were going to smash you they should have a tiny bit of lag leaving them open for 3 or 4 fists sending them off the edge then you can go straight into edge guarding from there. Peach is very light and can be sent off the top and sides very easy at around 70% with side and up smash attacks with no charge but at around 85to 90 the dsmash will usually send her granted her DI skill. As for approaching her, short hop in but the last jump when your closest fast fall and air dodge to avoid her up smash, it can do great damage granted they hit the sweetspot but if she misses it has nice lag time so superpunch is there, or Usmash to get her into the air and you can work your aerials from there
hope this helped and if you need any other help with tough matchups post it because theres a ton of good wigi's around here that can give you several points of views