If our lovely GM's dice rolls try to screw us over,

I'm for options 2 and 4. With 4 being preferred.

Fenna is injured, but it's her shoulder that needs treatment in the hospital so she can walk. This does mean swimming is not an option for her. The other injuries were also in her torso but they're healed enough to walk and scout at this point, even more if they rest fist.

We can definitely use Sil for distractions (her Loud Screech can distract enemies) and for sending messages. With real enemies approaching, guards aren't going to pay much attention to a bird of prey.

Fenna is not keen on turning back or do any kind of fighting. In character she is very set on getting more information about the reason they're here, and they're very close to finally getting that message that is waiting for them. She also really wants her shoulder treated and the nearest hospital is in Valheim. So she doesn't want to travel to another city and lose more time. Waiting for the cover of the night is a sensible idea and she will agree with that.

Would waiting for midnight or early morning (before the sun is up) give Clive enough time to go to Cherrad and return?

I like option four as well, Undaya blessing grants waterbreathing so we should be able to sneak under the river.

We could also divide into two groups, a ranger, a bruiser and a mage for each, half sneaks into Vallheim and the other half move for reinforcements, Sil should be able to keep us communicated

@ZapdosIt'd be up to the boss man on that one.

To add to what others have said; I'd say Clive should take some gold to sponser the journeys of the prospective 'Cherrad messengers.' The closest city that could have reinforcements might not be too far for the one messenger. Capitol City, however, might require a long trip - like, weeks maybe - that needs resources, so a gold piece or two, might go a long way for the other messenger to take up the big task.