Ignore the haters on this forum, some have been here for too long and belittle people seeking help.
There's a learning curve for everything.
As long as you don't make the same mistake as before that's fine.
If you want them to leave your home immediately then just pay final salary/notice and buy them a one-way ticket out of HK to their home country + transport allowance.
Do not pay them cash for the ticket, buy the airfare for them otherwise they will stay illegally in HK and not leave.
It is fine to hire multiple helpers, you can begin hiring process immediately.