To be clear, my information is on Henry Rickman and Mary Kate Collins, who married in Waterford and subsequently moved to Fulham, West London. It is they whom Alan Rickman descends from.
Mary Kate's father Denis was indeed a retired Army pensioner who served in various places in the 1800s such as Madagascar and the Crimea, and received a number of medals. I am in possession of his military records. His marriage to Mary Quinlan was his second marriage, and he had a series of other children in Scotland prior to marrying Mary who was over 30 years his junior at the time of the marriage. I have numerous official records of both the Irish and the Scottish Collins families and of Denis, and also a number of family stories that have been handed down, which I am very happy to share.
I have no information on Alfred Rickman, sorry.
Thanks!