Do you know aht, if any commodity code they should be travelling under, this will be your first port of call. At that point you can then check if there are any export licnses required, such as if they fall into pre-cursor goods, or possibly dual use items (check SPIRE for that – happy to help as i have access).
Then assuming no issues shipping out, next thing is for the import. It will need a T1 doc at minimum, stating the commodity codes etc – this will then need the import version for Luxembourg checking as you did for exporting for the UK.
If you know the commodity code, let me know and i’ll dig around.