I decided to plant some marrow seeds this year. I planted 5 pairs of
seeds and sacrificed the rubbish ones for the greater cause. I now
have 2 plants, one is small but has a lovely marrow growing out of it,
the other is massive but every time I think it's going to sprout a
marrow they just shrivel up and die.

My questions a

1 The marrow that is growing is a bit of a funny shape and doesn't seem
to be filling out to a proper marrow shape (it's really narrow at the
top). Is there anything I need to do (other than plenty of water) to
help him along?

2 Is it possible that the massive plant is taking up all the water and
the good bits from the soil? Is it worth considering culling it to
give my smaller plant with a marrow a better chance of full marrow
shapeness (Ok so I might have made up a word there but you get the
idea).