I don't know what to tell you immediately about Falco. His pressure is insane, and beating Falco isn't so much a matter of 'beating Falco' as it is a matter of 'beating the player'. My experience comes from a un-experienced, but technically proficent, player, which isn't very helpful for advice giving sadly.
If you get the impression that the moment your particular Falco is committed to attacking you, you could try to roll when you suspect a Nair/Dair/Dash Attack on his end and possibly retaliate with your Nair.
If you spot Falco not going for short-hop single laser and tries something like a double laser, it's possible to Quickdraw on reaction and hit him.
The main thing you want to remember is that you have the Uthrow chain grab. You can very easily get a kill off of it by finishing off with a Bair into edgeguarding.
Someone else is going to have to give legit advice on solid Falco tech.
Sonic? Um, I've played 2 players who play Sonic. Both I beat badly. Possibly also don't have good advice here.
One of the Sonics I play is incredibly aggressive, if you've got a similar thing then dash dancing + retreating Nair/Fair is a very good option.
...Yeah, I'm not sure what to say since I honestly feel Ike is a character that you play players more than characters. Both those Sonics I played for example were entirely different and I played them differently for it.