As others have said, it is not possible to re-home any of these horses. You could “re-home” them to someone who would quickly get them on a truck to auction, but that’s about it. Overall I think it would be irresponsible to try to pass them off on someone else. As someone else mentioned, I don’t believe any of these horses sound like candidates for a therapeutic program.
In the short term, get a farm sitter and go on vacation. There’s no question about that.
For the long term, I have zero judgement for you should you decide to euthanize. You didn’t mention the ages of these horses, but horses can live to be 30…35, and your feral pony will probably live to be 40. That can be a lot of years of responsibility and a lot of $$$, especially where three horses are concerned. I encourage you to add up the money and time as part of making a clear-headed decision. Horses are far more expensive and time consuming to care for than dogs or cats.
Anyway, I think it is perfectly fair for your husband to question both the expense and the time commitment/responsibility as it has a very real effect on him. Time and money, preparation for retirement, whether or not you even want to live on a farm anymore, and the health of your marriage/your husband’s feelings are significant real life concerns that you are allowed to consider. Especially if after all the time and expense it is not even enjoyable to you. I think it is very fair for both of you to discuss how many years of retirement you want to invest in for these horses.
@OverandOnward 's post has a lot of wisdom. I’d like to agree/emphasize that this is a really personal decision and not something that other people have a right to judge. We all do the best we can by our animals, and a peaceful passing after some years of pleasant retirement is a life well lived for a horse.