ok. Personally I would get a flight down without the kids and spend time house hunting. Paper called Rueda de Negocios comes out 3 times a week is the best place for accom ads,be aware you will never see the price published so always have to waste time and ring.
Could strike lucky and find somewhere quick or could take a fair while, might be ready to move into , might be available in a month...
San Blas, very pricey. Nice residential area is Magisterial, 10 to 15 mins from centre in taxi ( traffic can be very bad) house will cost you prob 550, 600U$ upwards. May not be particularly nice, and as in all of cusco, windows will be small and ill fitting, probably a cold tiled floor, roof may not be finished, neighbours may decide to build a 5 storey block of flats in front of your sunny window.
Apartments say 3 bed newish go for 350 to 500 U$ depending on location and what the owner fancies charging. Equally you can pay 450 U$ for bad condition 25 yr old flat that owner has decided is worth that amount because they know of someone who once charged someone that.
standard of houses is poor really, especially for the price. many places get not sun and are cold due to bad design. Hot water usually powered by dodgy shower head with wires all over the place. Walls rock hard concrete.
Schools: Ausangate has good rep with lots of gringos but many find it too laid back ( bit montessori), not enough homework or old style education about 450 soles per month. Puclasunchis ( not quite spelt like that), also has a good rep as an alternative school, 400 ish soles. La Salle prob the best more disciplined school, 350 soles month. Catholic mixed, good though has it stupidities at times.Lots of homework and push kids hard but fairly good sportwise( for cusco) and meant to be moving to a new bigger site soon.
hope that helps