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This is not my speciality but having work in the same office as some PhD students in malaria some understanding has rubbed off. Not sure you like to hear it but your problem is not un-commom. There are various reasons for this and the best next stop could be the Malaria centre at the London School of Hygiene and Tropical Medicine or similar as you probably will need and Entomologist to identify which kind of mosquito you have.
Various strains of mosquito's have different biting behaviour. Some bite at dusk when people are not yet under their bed net which might be your problem. If that is the case you have two choices. Campaign for them to go to bed earlier or find an additional protection strategy. Depending where people spend their time during dawn you can design a house spraying strategy.
2-3 nets a person seems a lot ;-) In particular as not everybody needs a bednet to be protected. There is a mass effect which makes that those having a net (and serve as life bait) protect those not having a net although it was not clear some year ago where the cut-off point in coverage is to achieve that mass effect)
Kind regards Kristof