Ah yes, this is a difficult one. It is likely different depending on the country you live in and the laws, but - even if you wanted to - it is essentially not possible to force your parents to accept help. It is very difficult for a person to be deemed incapable of making their own decisions and this is the only way these types of decisions can be made on their behalf.
So, you can just continue to keep an open discussion with them about it - encouraging without pushing too hard, as we know this often backfires! Maybe let them know your boundaries if you are providing care a paid caregiver should be doing; that you cannot do this long term. Also, you might ask a social worker to assist with this discussion if it is difficult.
It is great to be proactive but it is a fine dance, for sure! Respecting a person's choice to live at risk can be the hardest thing for any family member.
Good luck with this and let us know if you come up with anything that works well with your folks.