Cracked sandstone lintels, repairs?

[peter1450]

Untitled

• peter1450
• 28 Jan 2010
• 2

Untitled

• peter1450
• 28 Jan 2010
• 2

Replacing windows in an upstairs bedroom with a bay. Having removed the previous owners/window fitters idea of making good i have discovered that two of the three sandstone lintels of the bay are cracked through the middle ( see pics).
What I would like some advice on is can they be made structurally safe by myself and if so how or do i need to have them professionally replaced before the window installation. The cracks appear to have been there for some years and have been bodged previously with some kind of concrete poured into the back of one of them .
Thanks in advance Pete.

 

[PrenticeBoyofDerry]

More pictures further back so can see more of the lintel and underneath.
Looks like stone work and not a lintel, can we remove the curtains?