select p.CompanyName,p.ResidentialAddress 'Address',p.DateOfBirth,p.Age,p.PhoneNo,p.MobileNo,p.Education,
pr.Profession,Lst.StateName 'Living State',Lct.StateName 'Living City',Nst.StateName 'Native State',
Nct.StateName 'Native City',f.FatherName,f.MotherName,
sum(cast(f.BrotherMarried as int))+sum(cast(f.BrotherUnmarried as int)) as TotalBrothers,
sum(cast(f.BrotherMarried as int))+sum(cast(f.BrotherUnmarried as int)) as TotalSisters
from personalinfo p
left outer join Profession pr on p.Profession=pr.id
left outer join state Nct on p.NativeCityId=Nct.id
left outer join state Nst on p.NativeStateId=Nst.id
left outer join state Lct on p.LivingCityId=Lct.id
left outer join state Lst on p.LivingStateId=Lst.id
left outer join familydetails f on f.customerid=p.customerid
where p.CustomerId='a1a57b79-6585-406f-a5a0-53cf7b9f3f60'
here your using some aggregate functions, so you must be write a Group by clause with all selected parameters except that aggregate functions.
select p.CompanyName,p.ResidentialAddress 'Address',p.DateOfBirth,p.Age,p.PhoneNo,p.MobileNo,p.Education,
pr.Profession,Lst.StateName 'Living State',Lct.StateName 'Living City',Nst.StateName 'Native State',
Nct.StateName 'Native City',f.FatherName,f.MotherName,
sum(cast(f.BrotherMarried as int))+sum(cast(f.BrotherUnmarried as int)) as TotalBrothers,
sum(cast(f.BrotherMarried as int))+sum(cast(f.BrotherUnmarried as int)) as TotalSisters
from personalinfo p
left outer join Profession pr on p.Profession=pr.id
left outer join state Nct on p.NativeCityId=Nct.id
left outer join state Nst on p.NativeStateId=Nst.id
left outer join state Lct on p.LivingCityId=Lct.id
left outer join state Lst on p.LivingStateId=Lst.id
left outer join familydetails f on f.customerid=p.customerid
where p.CustomerId='a1a57b79-6585-406f-a5a0-53cf7b9f3f60'
group by p.CompanyName,p.ResidentialAddress ,p.DateOfBirth,p.Age,p.PhoneNo,p.MobileNo,p.Education,
pr.Profession,Lst.StateName,Lct.StateName,Nst.StateName ,
Nct.StateName ,f.FatherName,f.MotherName