Where did they settle in the US ? - most of the US bound emigration was from the northern parishes (many families had uncles etc who could provide job introductions and help) thus it would be good to see where he settled (Manx tend to be like starlings - they flock together for mutual warmth + support) - have you located them on any manifest - if they married on arrival in US then either a ship board romance or she was waiting for him (or he her which is more likely) as otherwise why not marry back on Island among friends + family.

If I have the correct family in 1841 - at Close ne Calley Andreas - then Wm snr was a weaver - it would be quite unusual for a younger son to inherit land