A peerage in the United Kingdom is an aristocratic title which confers the right to sit in the House of Lords, the upper chamber of the legislature (parliament)

A peerage in the United Kingdom is an aristocratic title which confers the right to sit in the House of Lords, the upper chamber of the legislature (parliament). Historically, peerages were hereditary titles passed down to the eldest son. In modern times, peerages are usually appointed for life terms by the government. What I find confusing about the article is that it's not clear what it means by "her brothers were 50% less likely to enter parliament". Parliament being ambiguous here. If this refers to entering the House of Lords, then at most one brother (the eldest) could do so upon the death of their father. Is it really saying that the shame of their sisters marrying down dissuaded heirs to peerages from taking up their birthright seats? Seems odd. Alternatively, is it suggesting that second sons and heir-apparents were standing for elections to the House of Commons (the lower chamber of the legislature, also parliament) and became less successful as their standing dropped?