What happens when two people with double-barrelled surnames (e.g. Brown-Robinson) marry and what do their children do. What is the record for the most surnames in genuine use by one person (excluding wind-ups, comedies etc.)?

In answer to your question - In the UK the female partner may take whichever name she decides to adopt on marriage The male will retain his original surname unless changed by agreement. The children also have the legal right to change their names (by Deed Poll) to whatever they want to be known as.

My GBR give the longest surname as six barrelled and the longest without repetition as 5 barreled Lady Caroline Jemima Temple-Nugent-Chandos-Brydges-Grenville (Lived 1858 to 1946)

Surely if Miss Black-Brown marries Mr. Smith-Jones then she becomes Mrs. Smith-Jones and the offspring are Master/Miss Smith-Jones. I appreciate that some women are loathe to give up their maiden name and so add it to the husbands to make a double-barrelled surname but if they were already d-b before wedlock then they would have four surnames and become some kind of laughing stock!

In some countries, when a couple marry they both retain their last name. When children are born, they receive the last name of the mother. I believe it is
because they were connected, making them a part of the mother's body and eventually coming out of the mother's body. I agree, the hyphenating thing can get way out of control after just one or two generations.

In Ireland, a woman may choose to change her name when she marries or she may keep her own surname. Whatever she chooses, the children get the same surname as the father. If you want the children to have a double-barrelled surname, the father must legally change his surname to the double-barrelled one before the children are registered. He may change it back again afterwards if he wants. What many people do is to give the child and extra given name: Joe Smith marries Anne Jones, the child is called David Jones Smith, where David and Jones are given names and Smith is the surname. Then you call the child David Jones-Smith and treat it as a double-barrelled name.