In a warm home, swordtail or guppy fry will be fine without a heater. A 2 gallon bucket is better than nothing but is not a good long term home for growing fry. You need to work out how you will be looking after them next week as well as today. As has been said, massive daily water changes can allow the fish to survive for a while but something must be done to stabilize the situation. Otherwise, the first time you do a water change late or forget one, the fish will be in trouble. Good functioning filters are not an absolute must have but the care it takes to look after the water without one makes success without a filter very unlikely in the long term.
