Well, Luster could be wished up so that'd be safe enough - or some Elves could come live on Nest, but Elves who are interested in raising children are generally themselves pretty embedded in their communities and families and not so thrilled about leaving them -

...okay, if they can live in Luster and have pools for their passengers and people will not be scared of them and the Elves will help them with their kids and the kids of the people who do not want to accompany the migration that will be all right.

Yeah, that can be accomplished. ...maybe they should start out in Luster's Valinor so they have time to get used to the idea before the babies arrive, can Elspeth sell Luster's Valar on that?

...she can explain the situation, but she isn't that strongly advantaged in convincing people of her value judgments and she doesn't even strongly have a value judgment on the correct upbringing of the forthcoming kids.

No the thing the Valar need convincing of is not that Elven children should be brought up by parents who wanted to have them and want to stay together and give them a stable home, the Valar already agree with them on that, the thing they need convincing of is letting a non-Elves species into Valinor in the first place.

...Elspeth being a non-Elf species who Valar are generally pretty happy to receive she can probably sell them on that as a general principle.

That would be good! Then they can have ten times as long to acclimate Yeerks to the concept of babies!

So Elspeth goes to tell the Luster Valar what's going on.

The Luster Valar will consult Eru on this.

Eru thinks this is fantastic.

Okay. The Luster Valar will allow it.

...did Eru comment on why it's fantastic?

He did not!

Is that not the sort of thing they ask? Elspeth is curious about why Eru thinks this is fantastic.

They don't tend to ask that, no. The answers don't tend to be very explanatory. They ask.

Eru apparently thinks that it is material for a good story.

...Elspeth thanks the Valar and relays this vaguely worrisome information.

That is some vaguely worrisome information, yes.

But anyway Yeerks can live in Luster.

...okay. Well if anything disastrous happens it'll probably happen on Valinor time.

Probably!

And within range of Wish.

The Yeerks will take their cues from the Elves on how worried to be about Eru storifying them.

Eru likes storyifying things but Yeerks have free will so won't end up doing things they're not okay with. 

Okay cool.

So they pack up and say goodbye to their friends and move.

And Luster is wished safe from them by some concerned Valian Elves and now the rest of their pregnancy will drag out most of a Year so there's lots of time to get used to the idea.

It sure takes getting used to! See, usually, when Yeerks reproduce, they just glom together with several of their friends and then separate into one to two hundred offspring, killing the parents in the process!

That is completely horrible and appalling and why would anyone ever do it and who looks after the babies?