Integration problem in terms of reals returns complex result

Questions
,
1

How can I get an answer in real terms?

$Assumptions = (x|y|z|a|b|c)\[Element] Reals

p:=Sqrt[(a-x)^2+(b-y)^2+(c-z)^2]

I1a= Integrate[a/p,b]//FullSimplify

I2a =Integrate[I1a,c]//FullSimplify
2

This combination gives a real expression:

Simplify[ComplexExpand@Simplify[I2a // TrigToExp,
    {a > x, b > y, c > z}] /.
  
  Arg[u_] :> ArcTan[ComplexExpand[Im[u]/Re[u]]]]
3

Thank you. It works really well.