I can't think of a sure-fire way of doing this, but if you call at T-72 and again at T-48 you may be to head off anyone else wanting that front set of seats, but clearly Orlando is going to be popular with parents. Because this can only be tentative, and in view of the distressed caused, would it not be better to get a block of 4 further back, accepting the loss of the bassinet, and then at T-72 see what happens? The obvious downside is that you in overall terms reduce the chance of getting a bassinet, without totally ruling it out, but greatly increases the chance of being sat in one group (though of course that isn't 101% guaranteed either). It is a night flight, so being just one row apart, when hopefully you'll get some sleep, isn't the worst outcome either.