Yes — all three can be hand pollinated, though the method and usefulness differ by crop.

Eggplant 

Eggplant flowers are usually “perfect” flowers (they contain both male and female parts), so they often self-pollinate with wind or insect vibration.
Hand pollination can help if: flowers are dropping, fruit set is poor, temperatures are very hot or cool, pollinators are scarce.
How: Use a small paintbrush, cotton swab, or even an electric toothbrush. Gently touch inside an open flower to move pollen around. Or tap/shake the flower stem lightly around midday.

Best time: Late morning to early afternoon on dry days.

Peppers

Bell pepper and hot peppers also mostly self-pollinate.

Hand pollination method: Lightly shake plants or flower stems. Or use a small brush to transfer pollen between flowers. Helpful during: high humidity, greenhouse growing, very still air, extreme heat (>90°F), which can reduce pollen viability.

You usually do not need to transfer pollen between separate plants unless you want crossbreeding.

Squash

Summer squash and winter squash are different because they produce separate male and female flowers. You often need hand pollination if: bees are scarce, fruits start growing then shrivel, rainy weather limits pollinators.

How:

Identify male flowers: thin stem behind flower, contain pollen-covered stamen.

Identify female flowers: tiny baby squash behind flower. 

Pick a freshly opened male flower in the morning. Remove petals. Rub pollen directly onto the center of the female flower. You can also use a soft brush instead of removing the flower.

Best time: Early morning, when flowers are fully open.

A few extra tips for Maryland-area gardens right now: Avoid overhead watering during flowering. Keep plants evenly watered; stress reduces fruit set. Hot spells above ~90°F can temporarily reduce pollination success in peppers

Good luck

Len