Ok my best friend was 25 when his now wife went to work for him at 17 yes he was hitting it but they were both different people then most.
She had had a hard life and was very mature for her age, we went out many times before she turned 18 and they got married. They have been married now for 19 years and have five kids.
She and I have talked on many occasions when I stop buy to drag him out to shoot his 45 that I tell him is getting to dusty, she does not regret anything and feels that this is the life that God intended for her. Sports MOM, ballet MOM, and Wife to her husband.
She rules the house, my friend rules his business. When he sold the shopping center he told me that if he didn't want to he never had to work again and he was thirty.
She harps and hounds about spending money at home as she sees this as part of her "job" to make sure they can take care of all the bills, she loves going with my wife to shop the consignment stores for clothes.
These are people who could be driving any car they wanted to but she got pissed when he went and brought her a red Monte Carlo ss for Valentines day a couple of years ago, just so she had a "HOT" car to drive when he was running the kids in the van.
I do not know your brother or sister in law so I cannot judge them.
Remember that in earlier times here in America women were getting married at 14, and could handle the life at that time.