A lot depends on who you will have looking after things while you are away. If it's someone very experienced who can live in, then not such a problem. If you don't have anyone like that you can call on... :/
I'd get the tup out now, so at least you know that lambing ends at the beginning of June. So then the youngest lambs will be nearly 4 weeks old and past the early danger time, unlikely to get rejected.
Then consider whether you might be bottle-rearing... personally I don't like to wean them before 6-7 weeks, although I know many wean at 5 weeks. Personally, if I didn't have an experienced sitter, I wouldn't really want to be away for the couple of weeks after weaning, as I watch them closely to be sure they're doing ok on their non-milky diet. Although I guess just being away for say 3 or 4 nights they couldn't come to too much harm... :/. Unless they overdo the grass or cake and get bloat, of course.... Many find that bloat is more of a risk before weaning, but given your timing you could get past that stage.
Other things... when will you shear? Will the sheep need an experienced person watching for and dealing with any flystrike? It's Manxes you have, isn't it? I've had at least one lamb every year get bothered by flies on the horn, especially if the lamb has managed to damage the horn. You could decide to dag, worm and Crovect (horns as well as fleece) before you go, which should keep problems at bay for a week or so!
What about orf? If you have it on your farm you could Scabivax them all. If you don't know yet whether you have it, though, you probably won't want to use the vaccine as it will introduce the disease.
The other worries would be mastitis, and/or lambs starting to fail to thrive, getting diseases as their passive immunity wanes... You could Ovivac the lambs at three weeks and again a month later, and do your trip towards the end of the month period. (But then getting into more risk of strike, and/or the shearers coming...)