Tomatoes don't need insects for pollination. Brandywine is well known for being a stingy producer. You don't mention where you are, how you are growing them, nor the temps or humidity you have right now but you should check out the FAQ on blossom drop over on the Growing Tomatoes Forum.

Cucumbers and zucchini have separate male and female flowers on the plants. The male flowers have just a skinny stem behind the flower whereas the female flowers have a tiny fruit attached. You need both flowers open at the same time for pollination to occur. If you do have both male and female flowers and still getting no/minimal fruit then it is likely a lack of pollinators and you might want to hand pollinate. A search here or on Google/Youtube will tell/show you how to do that.

Rodney