Hello,
if TIFF contains a single page you could write:
with TImageEnView.Create(nil) do
try
IO.LoadFromStreamTIFF( inStream ); // is inStream at position 0? Otherwise you need inStream.Position := 0
IO.SaveToStreamJpeg( outStream );
finally
Free();
end;
// now reset outStream position and read it in your image component
outStream.Position := 0;
...etc...
That code also assumes the original TIFF is 24 bit RGB, otherwise a color conversion is necessary.