Some remaining questions

Was Moira already married to dr. Nicholson when she murdered the millionaire? If no - why would she afterwards get married to this guy to live in some horrible mental institution, and not marry her presumable true love, the single Roger Bassington-ffrench, and enjoy all those millions from the inheritance? (under a new identity if needed) or just leave Britain?
If yes - how did she set up the whole Templeton estate with a fake husband, parlourmaid, gardener, cook, for months, presumably in some village where everyone would know about a new wealthy family moving in, all without rousing any suspicions after the dead of a famous millionaire at their estate who also left them all this money? What did her husband think she was doing all that time? If Moira seduced the millionaire in the hope of gaining his inheritance, than why did she pretend to be married with her fake identity of Templeton instead of being single? The whole plot would presumably be much easier if her fake-identity was single?
Why didn't she leave dr. Nicholson after getting the big inheritance?

Why did Roger Bassington-ffrench murder his brother when he would presumably gain nothing (since the brother had a son to inherit the estate and a wife to be the son's guardian and the wife had her own love-interest already) AND he already got the millionaire-inheritance together with Moira?