I don’t know you, your family or any other details bar your OP but it strikes me that you need to invest your energy helping your lads out rather than looking for a way out of the country. I can see the attraction in starting afresh somewhere new, but im pretty sure that you would end up in the same situation in a short space of time, just in another country.
Your lads who are into drugs and have no motivation won’t suddenly change when you put them in a different area. You may have a honeymoon period but they’ll soon revert to their old behaviour no matter where they are in the world. You need to address their behaviour and help them change their outlook on life. This is all easier said than done, but at least in the UK you will have people to help you. You mention that one of the boys is known to MH services, if he has a key worker ask him what can be offered to help him. You could also ask for advice from drug services/charities that will be in your area about a strategy to help your boys out.
Good luck with it, as a parent myself I can appreciate that you have some tough times ahead.