What's the Name of That Book??? discussion

I read this children's semi-fantasy novel in the 1970's but it was my mom's friend's husband's "favorite book as a kid," so was probably from the 1930s or '40s. The scientist? inventor? father of two sisters is kidnapped by a neighboring country. First, they are so upset they eat so much, they gain lots of weight until someone on the street mistakes them for balloons (yeah, it was the 30s), then they cry until they lose all the weight until someone mistakes them for needles?, then they decide to actually go find their father. They sneak onboard a moving truck full of furniture, and during the weeks(!) of travel, they move the furniture around to make a comfy place to hang out. They finally arrive in the other country where the king? has put the father to work for him. Hijinks ensue that I don't remember at all, but they of course get their father back and everyone home safely.

The Wind on the Moon seems to match?

Oh my gosh, I think it might be!!! Ordering now...

Google Books preview of The Wind on the Moon by Eric Linklater - Ayshe's suggestion:

- https://books.google.com/books?id=Qn5...
- There are different cover images.
- It contains distinctive black-and-white illustrations.

Quotes from the book:

- ... they ate whatever they could find, such as cold chicken and hard-boiled eggs and custard and plum tart and a slice or two of cake.
By and by they grew so fat they were almost completely round, like balloons.
- As soon as they saw Dinah and Dorinda, they all shouted at once, 'Balloons, balloons, balloons! Look at the big balloons!'

SOLVED!!! Thank you, Ayshe, for the name suggestion, and thank you, Kris, for the preview--I read the first few pages, and I remember the luggage packing/stomping scene. This has been bugging me for YEARS... I can't wait to read it to my kids!!!