Can anyone advise? A good friend (farang) of mine is about to marry a Thai lady. They are worried that she would lose the benefit of the 30 bt scheme as she is under continual care for a blood disease. Does marriage to a foreigner put the scheme in jeapordy?

No.

No.

She has no problem in getting care at the hospital she is registered now. If she moves to another town she has to register there and that may be a bit complicated as I think she has to be on a Tabian Bahn that is nearest to the hospital or clinic she is registered,

As mentioned, being married to a foreigner has no effect on her coverage. The only issue I can think of is if she changes her name to her husband's then it is important to get all her documents updated to reflect it. But she is not required to change her name if that makes it simpler.

Yes is no problem my wife is on it uses it every month..