Hi, I read your post this morning and I've been mulling over how to reply.
If you like shopping, then Douglas and Tynwald Mills is pretty much it. Although we do have a Waterstones and plenty of coffee houses, so your daughters should be happy
Watersports are very well catered for, there is talk at the moment of an artificial reef being built for diving. If your children are sporty, the Manx government are very keen on promoting sport for children, there are many clubs, the NSC (National Sports Centre)in Douglas has a lovely swimming pool and there is also a gymnastics centre. There' a brand new pool in Ramsey, not had the chance to visit it yet.
Food - I had a lovely meal at The Garrison recently, although they do have a reputation for poor service. We tend not to eat out in an evening as we don't have a babysitter. But this website has good recommendations.
[http://www.wheresgoodtoeat.com/Restaurants.asp?EstcountListPage=1&CommentsPage=2&ID=569]
For lighter cafe type meals, I'd recommend The Alpine (fab Sunday brunch and coffee /cake), it's opposite the PO in Douglas centre or The Velvet Lobster on North quay in Douglas.
The Sound is worth a visit, it's in the south of the island , it has a cafe with fabulous views onto the Calf of Man. there's pretty much always seals. Killer whales have been spotted recently (take your binoculars).
There's also the Point of Ayre, which is the North most tip of the island. There isn't actually anything there, bar miles of pebble beach, Arctic Terns and a lighthouse, but it's wild and desolate.
Laxey beach is lovely at low tide, but I guess you've seen that as you have friends there.
Mooragh Park in Ramsey is worth a visit, depending on the age of your children. pack a swimsuit for the kids as there is a water park, plus boating lake, good playground and crazy golf.
You mentioned St. Johns, yes, that's a nice area. There are two schools there, the Bunscoill Ghaelgagh (a Manx language school and St Johns Primary. Both are well thought of and both feed the secondary school in Peel, which again has a good reputation. We live in the next village to St Johns.
I'm not sure of the age of your children, but I moved here with a 2yr old and found it quite difficult. There isn't a lot for children of that age, apart from soft play (there are two) or toddler groups. But for school age children, there's a lot more. In winter it can be quite difficult as it's really a case of make your own entertainment.
There are walks in any of the National Glens, which are beautiful.
[http://www.gov.im/daff/countryside/country/nationalglens.xml]
Health care here is brilliant, but I guess you have inside knowledge there ;).Education is good. There aren't really many security concerns and that's worth a lot. Travel to and from the island can be expensive - complaining about the Steam Packet (racket) Company is a national pastime.
Not really sure what else to say.
Feel free to email me ixia at graffiti dot net.