I think three nights is too long for a first time tbh
we left all three for one night the first time, ds1 was 19 (uni, driving vair sensible) dd was 16, also sensible and ds2 was 14 (.... when given unlimited console use is no bother)
we went mid morning, stayed one night and got back next day late afternoon...all was well, and they had supper under control!
I think we left ds1 on his own for a weekend at 18, he had a friend over and apart from finding sweetie papers hurled about the sitting room all as well then too
Having said that we often said when the ILs or my mum came to mind them that they were purely there to prevent me being pilloried in the Daily HateMail should anything dreadful happen. My mother is hopeless in a crisis, can't use the range, or light the fires, work the ansamachine or the heating.
Sooooo to sum up, I'd certainly leave him, but maybe not all on his own for the whole time, but from your later post he seems to be able to manage to feed and ten to himself. WOuld the house sitting HT be available for a day or two inthe middle??