I am afraid that you post contains a very large number of errors. Correcting these will certainly help you in your quest.
There are two Ravensworth Castles in England, one in Tyne & Wear and the other in Yorkshire. Both are in ruins. Neither has been converted into a museum. Neither has any connection with a family called Walden.
Loughtee is a barony (a geographical subdivision) of County Cavan (note spellings), which is in Ireland, not England.
An estate in Loughtee, including Dromellan Castle, was granted to a Sir (not Lord) Richard Waldron (or Waldram) by King James I in 1609. The estate was sold by Sir Richard's grandson, Thomas, to the Rt Revd Robert Maxwell in 1664. It was renamed the Farnham Estate and remained in the Maxwell family until 2001. Farnham House (formerly Dromellan Castle) was turned into a hotel.