Firstly, we are having trouble with our internet connection so it may go off while I am trying to respond. If this is the case, apologies for the delay.
Now, to answer your questions.
If you were to apply for the following schools (for example) in the following order:
Your daughter would be allocated to the first school which, according to its criteria, would be able to take her. Therefore, if your daughter has a score that puts her in the top 500 (or thereabouts) candidates, she is likely to achieve a score for Chelmsford and would be offered a place there.
As far as Southend and Westcliff are concerned, you usually need a few more points for Westcliff than you do for Southend. Thereforefore, if your daughter, with the above choices, did not gain a place at Chelmsford but had the right score for Southend (she would need to be in the top 900 candidates or thereabouts, then she would be offered a place at Southend.
However, because Westclif usually require a few more points than Southend, if your daughter did not get the Southend place, then it is likely that she would be offered Sandon.
In the Southend area there are 150 places at each of Westcliff and Southend. 115 (maximum) of these places is offered to children in the catchment area who have passed the exam (obviously, in the order of points with which they passed).
The passmark is set each year at, purely for example, 100 and no child will be admitted below that passmark. In reality it means that if, in the catchment area, 120 girls score above 100, then 5 of them would not automatically be given a place at one of their grammars.
Next, the rest of the places are offered out according to the position in the "Essex order of merit" to girls who have put one or both Southend schools as a preference. It does not matter whether they live in Southend or Chelmsford or anywhere else.
The unfortunate thing about this is that the "order of preference" is not taken into account.
So, if you put down schools in the following order (again for example)
and your daughters mark gives her a Southend place but not Chelmsford or Westcliff, then your daughter will get the Southend place.
However, if a friend of your daughter has the following preferences:
and that friend achieves the passmark, she would not necessarily get a place at Southend, even though it is the first preference, because the places go strictly according to points achieved, no matter where on the preference list the school is. The only exception is that if you were to put the comprehensive above the grammar school and you were then to achieve the right points for the grammar you would not be offered the grammar.
As far as my opinion on schools is concerned, Southend is brillient. They are all good at getting excellent results but attitudes to the girls would appear different. Chelmsford, I have frequently heard, is only interested in medics, lawyers, etc and does not have great opinions of girls who aspire to much less. Westcliff is great but has had bullying problems in the past (so I am told). Southend respects pupils for who they are. It allows girls to develop their own tastes and abilities with encouragement but without pushing them into areas they are not naturally headed for.
The big difference between the grammars and comps, however, is that the grammars have extremely high expectations and there is praise only for those to reach those staggering expectations (in other words the A and A* all the way pupils) whereas the best comps praise and encourage each child for smaller steps along the way.
If you do not understand anything that I have written here or have further questions then please feel free to ask.