Cym -
I hear you about the older boys "hating" learning Spanish. I also hated learning Spanish in High School. Part of the problem was my own perfectionism. I expected "drill and memorization" to be fun, easy, and intellectually challenging - why not? I had coasted on my "quickness and big picture thinking" all through school up until that point.
Fast forward 25 years. My "dayjob" is in a setting were the majority of people are "more or less bilingual" and plenty are "stone cold" only Spanish Speaking. All my high school learning has floated back into use. I learned an awful lot back there. For the first two years, I re-learned a new word every day! Now most of my fluency is job related, and my syntax is English with Spanish words, but I sure can make friends and get work done in Spanish and pantomine. And if you had asked be back in high school I would have bet you 100$ that it would never happen. I litterally thought that there was something wrong with me. ((besides my spelling LOL))
So, Cym, let your kids know that skill learning is like the Bamboo Tree, dull but worth it, and fine to be "slow" at. It also helps if they get to interact with Native Speakers who like them.
Best Wishes,
Trinity