Capt Annesley Arthur Knox. Rappa Castle

Hi,
It was a while ago, but someone called Valda, wrote a message regarding the Mayo Knox family.

The information I have is as follows:

Isabella Jane Knox born 1855, in Mayo, married John Singleton Darlington 1880.

From notes, Isabella says her father was Capt Annesley Knox. It seems possible that the Capt would be the owner of Rappa Castle.

I came across a Harriet Knox who was also the daughter of Capt Annesley Knox.
I would presume that they would be sisters, but for a couple of things:

Harriet was born 20 yrs later than Isabella 1877 and she was born in India, not Mayo.

While of course this could be possible. Annesley could have been residing in Mayo at the time of Isabella's birth and it's not impossible that his wife (unknown) was child bearing 20 yrs later.

I have found no record, but he might have had more than one wife.

Unfortunately, despite trying IG, Family Search, Ancestry, I haven't been able to find the link.

Needless to say, any information would be graefully received.

Kind regards,
John