Yorokobi is a great song for them to sing together. It could actually handle a full group.
As for silly go round, that might be pushing it terms of capability. Since Haruna Luna and the other artist, I don't think they have the range to handle its ringer portion. Wakana is going to break the tone way too easily. Hikaru isn't going to be sweet enough, as well as boosting the sharp parts even more, when it shouldn't.
They should avoid inside your heart as well on certain portions for it is also too delicate. Same issue, through it can have more Wakana, it doesn't work for the others for clashes too much with the Haruna Luna, and the other artist. Hikaru is literally stuck between a rock and hard place on this one.
On the song selection of Nowhere, It isn't that they couldn't sing it. The problem with Nowhere is that could they have to do a full blown energy performance as well as being to improvise to the provide flair. The key to Nowhere is when and where to twist, rather than singing it. It's trickier in that sense. I don't think just singing it is enough to warrant this song into a fan selection here. There is a reason ,why Nowhere is treated the same as AnK is that the mastery of skill as well as being able to improvise on stage. The status is not for show, there is a genuine reason why they hold this song back until the end.
On Akatsuki no Kuruma, do not treat it as a FJY live. When they do that, the chances to failure are made even higher. It's closer to Akino and bless4 merry go round and Granrodeo collab as a semi-rough analogy. It is probably even rougher than that as well. There wouldn't be that much breathing room for they also have to be shuffling constantly. Once someone switches, the tone is going to broken by the slight change. It isn't hack sign world, where they get away. The other problem is the amount is that they will end up stealing FBM thunder to the song by being that large. Even with the band the blasting very loud, it may still become a major issue. It's hard to enough to hear the clarity in a orchestra version, this is literally making it worse in every way possible.
..They should have chosen a Saeko Chiba song instead.