in-pipe turbine meshing

Hello
My geometry which I want to apply mesh on it is an in-pipe turbine. There are two bodies: a turbine and a pipe. The blades are surrounded by a sphere that is subtracted from the pipe which indicates that different analysis should be applied on inside and outside of this sphere (figure 1). My meshing strategy implemented as follows: 1- An edge sizing which it’s type is element size (0.005 m) for the intersection of the blades and discs. 2- two edge sizing that their number of divisions is 20. One of them is applied for the blades’ edges and the other one is applied for the disc’s edges. 3- an inflation for the surface of the sphere. 4- A face meshing for the pipe. 5- a face sizing for the inner and outer pipe surfaces and inlet and outlet regions. 6- A face sizing for the sphere. 7- an inflation for the pipe’s walls (figure 6).
At last, the challenges are:
1- the inner volume of the sphere doesn’t mesh for small edge sizing (figure 4).
2- the maximum skewness is 1 (figure 7), the low-quality elements are placed at the location of the intersection of the discs and the blades (figure 5).
3- I can’t apply face meshing on discs.
I will be so thankful if you help me. Should I change my meshing strategy?