Barnabas's age wasn't mentioned, but I believe it was stated that he was born in 1770, which would make him 25 in 1795. Maybe Angelique really wore him out in Martinique.
I don't think any of Judith's brothers were 30 years younger than she, since I don't think Judith was as old in 1897 as Joan Bennett was at the time of playing her. (If so, then how old was Grandmama? And why didn't we see Baby Judith in 1840?) I think Judith probably was still capable of conceiving in 1897, because if she were not, I'm betting she would have felt she must disclose that to Trask when he proposed to her. Wouldn't that have been a touching scene for daytime drama!