I know that on the top table our parents are supposed to be split up so that my dad sits next to my fiancés mum and vice versa. Do we need to stick to this or can my parents sit together? I know how much my dad would prefer to have my mum the other side of him, mostly as he really is very nervous about his speech!
Sit people however you feel they will be most comfortable - I think it sounds like a good idea to sit your father next to your mother. You might like to ask your fiance to explain the reason to his parents so that they're not offended that your parents don't want to sit next to his!