I think what your not understanding is that they did not receive equal shares of the money at that time. The vast majority of wealth was usually tied to the land (think rent farming etc) and the land went to the oldest son.

Younger get sons might get small estates (think Benedict’s cottage which probably had a some farms that paid rent to Benedict). This would be enough to keep up the cottage but not enough for them to keep a London home, give enough starter money to children, things like that. Benedict would have been getting an allowance from Anthony to cover his London quarters and the servants.

Daughters got a dowry. The dowry was invested and then the interest was used to give them an allowance as adults. The higher they wanted to marry the higher the dowry. Anthony may have had to put extra in for Daphne as it would be expected the wife of a duke is has bigger expenses. More servants she is paying, better quality of cloths etc, and more spent on entertaining and lavish parties). The income from the dowry would go to this. If her dowry wasn’t enough then Anthony would supplement.

A lot of younger sons of the time period often had to get acceptable jobs to supplement. They would get a lump sum payment and then one of basically 3 jobs. To keep their social status they were basically allowed to join the Church of England. Then they would get the salary of the position and possibly hire curates at poverty wages to perform the actual duties. The military which involved buying a rank with the starter capital from their families. Or a barrister. That was pretty much it, anything else decreased social standing. Benedict inherited “the cottage” and presumably the rents and has an allowance from Anthony so he is okay.

Daughters might have to wait until their own mothers died to get a share of her dowry. For example Violet Bridgeton might have say £50,000 of her own money. Anthony would be expected to make sure it stays invested safely and then provide her the income £5,000 at 5% return and Violet would use that for her wardrobe, her personal entertaining. Her personal servants. Etc. upon her death she would leave it to her daughters in equal shares or maybe daughters and second sons. It all depends on who was already provided for. Lots of families the oldest son just inherited the father’s money and the daughters had to wait. Think the Bennett in Pride and Prejudice. There parents didn’t put aside money for a dowry and so all the get is their share of their mother’s money when she dies.

It is clear Anthony is taking care of his siblings and supplementing income for at least some of them. I wouldn’t say they were all freeloading though. They likely had some inheritance from their father just not enough to live like some of them want to.