Villagers don't breed even though population cap is not met

A naturally generated village in my survival world used to have a full population however there are now only two villagers left because they have died due to hostile mobs and they will not breed. I have tried giving them food and a couple of times they have entered breeding mode with hearts above them, but they then get angry particles and nothing happens. There are about 10-15 beds in total in the village so the population cap should not be met.