It is not necessary to join one’s feet with the next person’s while standing in prayer, however the shoulders should be joined and the rows should be straight and formed properly.
Hence, you may use your discretion about whether to keep your feet next to your neighbor’s feet or move it away—whichever is less distracting to you. If it is people that you know and regularly stand next to you then you may take them aside and privately discuss the issue with them.