Okay - first when is your 14 year old's birthday? Will she be going into year 10 in September or year 9? eg. will she be 15 before 1st September (year 11)?
Second where you live may have some influence, but not much. All schools in Guildford tend to be full. You may have to appeal to get your daughter's into your preferred school - I am assuming you are looking at state schools.
Are you Catholic? If so you can look at a wider area, and there are buses (but you have to pay) to St Peter's - if you can get your DD/DDs in to there.
If not the other schools are: Christ College, C of E but not as highly sort after as some of the other schools, but okay.
King's College - in a deprived area, but some nice places to live in the catchment.
Guildford County - a sort after school just outside the town centre, close by housing tends to be sought after.
George Abbot - a highly sort after school, Merrow and Burpham are highly sort after areas. (Also has buses from Send).
You need to apply to the LA ASAP.
Are you coming from overseas? Because the big issue is that years 10 and 11 are GCSE years, and children will have already chosen their options. Schools can work around this if they have to; I know George Abbot took one girl in year 11 this year and created a timetable so she could attempt 5 GCSEs, but it is not straight forward.
You want to get at least your eldest into school ASAP.
Guildford is basically a nice safe town, and even the more dubious areas are safer than lots of places. And even one large area of social housing I probably wouldn't put in even the dubious category.