If you want to remove the vengeful ballpoint strokes, it will be reasonably easy with the resynthesize plugin (included in Partha's builds, otherwise it can be added to standard Gimp). Start quick mask mode paint a thin white line over the strokes (this would be a lot easier with a tablet), exit quickmask, and use Filters>Enhance>Heal selection.
Blurry faces are due to poor focus, not much you can do about it (Instamatic cameras had fixed focus using hyperfocal)
There is a slight reddish cast on the picture. You can remove it or mitigate it using the whitebalance script, after sampling a white garment (even with shadows). Using it at full throttle is a bit brutal, but you can use a 50% color correction. You can also use the same operation to add a bit of saturation.
Blurry faces are due to poor focus, not much you can do about it (Instamatic cameras had fixed focus using hyperfocal)
There is a slight reddish cast on the picture. You can remove it or mitigate it using the whitebalance script, after sampling a white garment (even with shadows). Using it at full throttle is a bit brutal, but you can use a 50% color correction. You can also use the same operation to add a bit of saturation.