Are these containers microwave safe?

The listed specs do not say. Clear plastic food containers of this type are often microwave safe for reheating only, with the lid off, but check the base stamp before using one in a microwave.

Nothing in the specs confirms freezer use. Plastic containers this size are commonly used for freezing leftovers, but leave headroom for expansion and let them thaw before handling to avoid cracking.

Do the lids really seal?

The lids are described as leak-proof. On budget plastic sets, seals usually hold for sauces and soups but can loosen after repeated washing, so test with water before packing anything liquid in a bag.

About 2.75 cups, roughly a single serving of soup, a lunch portion of pasta or a pound of cut fruit. It is larger than a typical 16 oz deli container.

Can these go in the dishwasher?

The specs do not state dishwasher safety. Plastic lids and containers of this kind usually survive the top rack better than the bottom, and hand washing the lids extends their life.