ᐅ What type of insulation is recommended for a 50-year-old house?

My 85-year-old father is determined to insulate his 50-year-old single-family house (double-wall masonry) using blown-in insulation. It is a double-wall masonry construction. I believe that the 50-year-old plastic windows with double glazing, as well as the front door, should also be replaced. He considers that unnecessary, saying the windows are still in good condition and that they would only install double glazing again anyway. He doesn’t see an energy efficiency improvement there. The house is a detached single-family home with just under 100 m² (1,076 sq ft) of living space. The attic is unfinished, and apart from the glass wool insulation commonly used in the past, there is no insulation in the ceiling between floors. Under the roof tiles, there is a roofing membrane that was typically installed in the mid-1970s.

What do you think? And what happens if the walls are fully blown with insulation now and new windows are installed later, or if a patio door is installed instead of a window? Will the insulation then fall out again?