in 1904 103 Castle-Mona ave was a lodging house run by Mrs West - it probably continued as a boarding house post WW1 - you might find it listed in holiday guides, Electoral rolls might help but not all survived (try manx museum library@mnh.gov.im)
you could try iMuseum (www.imuseum.im) + newspaper search(tho you must pay) for any BMD that ref the addresses