The RMA doesn't govern peerages, but it does govern (or did) what marriages were recognized in British law, and by extension which children were recognized as legitimate.
Johann Leopold and Friedrich Josias both married against the RMA, therefore their marriages aren't valid in British law, making their children under British law illegitimate. Illegitimate children have no succession rights, be it to a peerage or royal title.
That the prince looses his place in the line of succession, okay, but by my understanding the Royal Marriages Act has nothing to do with the peerage titles. Would the Earl of St Andrews have married aganist the workings of the Royal Marriages Act, he would cease to be a successor but remains the Heir to his father's titles, isn't it?
The Earl of St Andrews would have remained his father's successor, but his children would have been illegitimate because his marriage wouldn't have been legal.
Evidence of this:
- Prince Augustus Frederick, Duke of Sussex
- Prince George, Duke of Cambridge
How could Leopold and his brother Andreas then loose their rights on the Dukedom of Albany because of their father's marriage contra the Royal Marriages Act? That can not be because of his father's marriage as the Letters Patent usually makes the peerage titles hereditary for the Heirs of the Body Male without furtherer conditions?
You're mixing names here.
- Prince Leopold, Duke of Albany was the son of Queen Victoria
- Prince Charles Edward, Duke of S-C&G was his
- Johann Leopold, Hereditary Prince of S-C&G was CE's eldest son
- Ernst Leopold was his eldest son (his son, Hubertus, would be the claimant to DoA today, if such a claim were valid)
- Peter is his younger son
- Friedrich Josias was CE's youngest son
- Andreas (current claimant to S-C&E) is his eldest son
- Adrian is his youngest son