Squash

I am growing some squash (winter and summer) in my greenhouse. Although I have been fertilizing the female flowers using a paintbrush I think that a couple of the flowers were maybe not properly fertilized as the tiny squash doesn't seem to be getting any bigger. I've got other squash of the same variety that seem to be growing fine. Do I just leave the unfertilized squash to drop off naturally or should I cut them off the plant?

I'm not surprised there are fertilization problems - it seems that all the plants (summer and winter alike) decide to produce either all female or all male flowers at the same time before switching. Don't suppose there is anything I can really do about that ...

You should be able to use flowers from courgettes, marrows or pumpkins to pollinate squashes and vica versa as they are all closely related and cross pollinate each other. The resulting fruits will be the squashes you expect but seed from them will produce hybrids.