I wonder if he has a rose-colored, nostalgic vision of his home country. He should not move -- with or without you -- until he has researched the realities: Can he really live on what that little store makes? What is the political situation, the level of crime in the area where he wants to be, the potential for increasing his income (because someday he might want to retire)? Does he have family members who are pressuring him -- are you aware if this is really all him or if he's not telling you perhaps that family members are pressuring him to return? Does he perhaps have elderly parents who need care and he's feeling regretful that he only has a short time left with them? You need to probe what is making him so intensely fixed on this that he would divorce you for it.
The fact you say he'll go with or without you -- wow, that got buried. Sounds like serious and intensive marriage counseling is needed but you never mention the possibility, and you're going to be a social worker, so it surprises me that you don't say you've told him you both need counseling before he makes any dramatic moves. I don't see any other option BUT couples therapy or counseling immediately, because he is entirely looking at only what he wants, not at what you or your children need.
And your kids? They will ALL refuse to go. You could force the two younger ones to move but they will resent you deeply for the rest of their lives if they are unwilling to go and you force them. Do you want that? Does he realize that the kids will resent him and possibly cut him off if he forces this on them?
And what about schooling? Where and how would they get educated, especially if they do not have enough Spanish even to cope everyday, much less enough to get the kind of education that will get them into college? Their education should be the absolute trump card here but it sounds like your husband has given that zero thought -- or is coming up with rosy scenarios like your teaching them at home. If he hasn't mentioned it, ask, because I'd almost bet that he's not thinking straight and has in his mind already pictured the kids getting an education from you somehow.
I would give him an ultimatum because he has given YOU one: He says "We go or I leave you and go." Now you need to say, "I love you but we cannot even discuss going until you agree to and fully participate in intensive couples therapy right NOW. Only then can we even discuss this." If he balks, tell him that the children do not want to go and he is putting his family there ahead of the children he fathered here and while you don't want to divorce, you do get a say in the family's future and so do your kids. Therapy, counseling, now, no further planning or discussion or decisions until then.
I know I sound unsympathetic towards him but I am married to someone from another country and he would never dream of putting his beloved family there ahead of his child here and her future educational prospects. I do get the feelings of separation, homesickness, etc. But your husband is in danger of moving back "home" to find he misses not only his family but the lifestyle he had back here.