How to distinguish between different types of squash?
If you want to post a picture somewhere I can probably tell you. 

You could do a cursory google image search and see if visually you can tell what they are. I have grown pumpkins most of my life and I have never manually pollinated them, I have never grown the "big ones" though so maybe that could be different. 

Pumpkins in the southern US generally ripen closer to late september-to-mid-october and can hang on the vines for a bit. It sounds like you have some veriety of squash. If you do have pumpkins unless they are an off shoot hybrid they should be taking on their orange color by now, especially if you planted them in spring. Having said that if they did not get enough water or enough heat then their growth would be stunted. It could be your yellows have stunted and are shriveling but I would assume they look healthy.