For spacing, your dtilt and bair are super good, but more than anything your movement is what needs to be getting them offguard. If you only dashdance and zone with bair, you will lose nuetral to half the cast, alternatively, if all you do is tons of DJC & wavealnding on platforms, a good half the cast can just start swatting at large areas above them, and will probably get you eventually. You need to mix in a variety of tools to be effective, and a large amount of them aren't going to be very intuitive.
For example, last time I was in tourney I had to play a good marth on FD, and lived to nearly 200%, and he was at 100ish. He was getting greedy with Fsmash, and I knew I could afford to risk my last stock, so I used downB in neutral to read his Fsmash and it worked. In 99% of situations that is a terrible option...
Similarly you don't have any single edgeguard tool that is super dominant, and you usually won't be able to cover all of their options. I think edgeguarding situations are often obvious when they're happening, and there is no shortage of aMSa showcasing tons of options available to Yoshi. If there is any specific area you're having trouble with that might be a better topic.