By actually doing weapon research in house, instead of buying foreign weapons. They have the resources for much of what is needed, and can make trade deals with each other to get what they need from their other cousins on the continent.
One example I would seek to research is high yield mini-missiles, particle projection cannons, etc. Instead of trying to catch up, go down their own weapon's development line that bypasses the road blocks put in place by the nations with the most military might.
So many of their sons and daughters who have gained educations in the degree fields that would be useful in this, should be encouraged to return home for high paying jobs and positions to boost their burgeoning military research.
That is my speculative opinion on how it could be done. Keep in mind that none of them are my countries and so not my business. So mine is an outsider's speculation, and not an insider's understanding of the present circumstances of their nations and the entire continent. They could quite possibly already have plans on how to deal with the future that is unknown to any of us.