Ilia will come along as well - the wilderness holds few fears for her (whereas Eudocia is probably freaking out, and undertaking a desperate accounting of the food & water stores on the boat).
Ilia is the only mage who has a spell for looking through the water, which allows exploration of other islands if she stays with the ship, and covering more ground (and more parallel adventures). Not saying she can't go but we don't need to send all the mages on every adventure...
who wants to play the tweedle twins? (or a different allocation of grogs?)
Abigail will happily explore the island, but she'll stay with the ship if asked. Her twin will stay behind regardless of the case. (Definitely not because I don't have her character sheet done.)
For the first island, I'll play one of my twins (or both if possible) and Argyros will stay with his sister.
So we'll have a more balanced party
As the ship approaches the second island, it appears somehow dark and foreboding, the trees barely alive as if some blight were upon the island. It is again mountainous, with a single peak rising from the ocean, and signs of some kind of dock on the eastern side.
Dock? Real dock or natural harbor?
If real, meaning there may be some people here, Aurore will go. Else Argyros.
We may need some guards more than the first island. Maybe Hector?
If we go anywhere on island two (can we have a name for it?), I'll play a grog. Captain is the last to leave the ship...
Please note you cannot take characters from the first adventure on the second- these are happening concurantly.
And yes, actual manmade dock.
Manmade ok. So Aurore will go on the second island if we're exploring it. And Argyros will stay on the ship.
Is Argyros not going to explore the bay on the first island?
Nope. I followed your warning. So there will be 2 magus and 2 grogs on the first island.
I've slightly lost track (very busy day at work yesterday) - which magi are going to each island? I don't mind at all which one Ilia goes to.
If I follow correctly for the time being :
First Island :
Alexander (Aqua'sMage)
Asilano mage (when finished)
Abigail (Lamech's Mage)
Tweedledum / Twedledee (Exu's grogs)
Second Island :
Aurore (Exu's companion)
Aqua's grog
Ilia ?
Though only 1 mage may be a bit short for the second island I could play Argyros. It's just that I want to play Aurore for social interactions. And I do not think it's wise (and allowed) to play both my mage and companion on the same adventure ^^
My mage is fine to move to the second island; it gives marginally more time to create him! I also have a non-existent companion who will be built first and can probably join the first expedition; and I suspect my grogs could be involved if needed (providing scouting on island 1 and muscle on 2?)
How are grogs handled? is it one player controls all grogs present?
Yes, one player controls all grogs.
Also keep in mind you can have mage-free adventures, for example if you want to set some grogs to hunting on the first island, or perhaps send along a plant mage to identify which plants are edible...
OK, in which case Ilia is on the second island 
Asilano, is your not-yet-finished mage likely to be any good with Intellego Vim? Judging from the first post, a spell to work out if we're stepping into an Infernal Aura would be useful. Ilia can cast this spell spontaneously, but not very well as she'll have to spent a fatigue level to cast it.
Intellego is definitely likely - it fits the concept- but we do have a couple of strong Vim magi already. I was planning more on Me/Co/An.
Mind you, Vim would also fit the concept well.
Ilia only has Intellego 5, so anything more than that will help To get things moving along, Ilia will try and look for an infernal aura, and leave the other auras to your mage.
And mine even if strong in Vim will never go into Intellego (at least no more than 5 if I want an apprentice someday). I hate intellego 
keep in mind that grogs are community property, and should be played by someone who has neither a companion nor a magus in that particular adventure...