Marx and Engels each seem to have had at least one brother in-law that they liked – Jan Carel Juta and Emil Blank respectively.
Jan Carel Juta was married to Louise/Luisa Marx. When the couple left Holland to settle in South Africa in 1853, encouraged by Juta's brother, (and where Juta subsequently built up a successful publishing company), they stopped off in London to visit Karl and family. Jan Carel suggested that Karl could improve his financial situation a little by writing for the bilingual pro-Dutch newspaper De Zuid-Afrikaan in Cape Town, with which he had been in touch.
When Marx wrote to Engels three months later, he referred to this suggestion:
What do you think of my brother-in-law Juta’s proposal, enclosed herewith, that we should write a monthly article for the Zuid-Afrikaan (Cape Town)? Rotten though Juta’s French may be, he’s a good, sensible chap. If only you and I had set up an English correspondence business at the right moment in London, you wouldn’t be stuck in Manchester tormented by the office, nor tormented by debts.
An article by Wessel de Kock on the Juta & Co website sets out Juta's commercial trajectory. Soon after arriving in Cape Town, Juta set up shop as "JC Juta, Bookseller and Stationer", which, according to an advertisement in De Zuid-Afrikaan, sold Bibles, hymn- and school books, periodicals imported by mail steamer, and, in addition, ladies writing desks, pen-knives, porcelain slates, Havana cigars and genuine eau de cologne.
He spent the next thirty years building up a publishing company. The unexpected death of his younger son in 1883 broke him and the following year he left for England, where he died two years later. I'm not sure what happened to Louise other than that she died in Rondebosch, Cape Town in 1893. Francis Wheen reports a comment from another guest who was present once when Louise dined at Karl's place:
"She could not countenance her brother being the leader of the socialists and insisted in my presence that they both belonged to the respected family of a lawyer who had the sympathy of everybody in Trier."
Engels was none too happy with his first crop of in-laws. In a letter to his sister Marie in July 1842, he wrote:
The noble young folk are rushing headlong into marriage, as if they were mad, and so blindly that they are knocking each other over. It is exactly like a game of blindman’s-buff and where two of them catch each other, they get engaged, marry and live in blissful contentment. Just look at your two cousins. There’s Luise Snethlage who has caught a husband [Hermann Siebel] who’s not bad but his hair is grey, and pretty Ida [Engels] has managed to get hold of one too, but I don’t think much of him either. True, he’s my brother-in-law, so I shouldn’t run him down, but I'm vexed that they didn’t ask me whether I wanted this Saint-Pétrus, this lion, this dandy, this Albert Molineus for a brother-in-law, and so he'll have to pay for it. I tell you-if you want a suitor like that, I'll send you a dozen every day and each day a new dozen. It was generous of me to let the whole thing happen at all. I should at least have protested about it.
.... I begin to despair of the human race; I shall become a misanthrope if you, Marie, you too -But no, you would not cause your brother such pain.
He seems to have approved of Marie's marriage to Emil Blank, however. In May 1845, he wrote to her, regretting the fact that he wouldn't be able to come to their wedding becasue of passport difficulties:
Anyhow you may be ‘Sure that I shall spend the whole day thinking of you and Emil [Blank], and that my best wishes will accompany you in marriage and on your honeymoon, although I shall not have the pleasure of expressing them orally. What I wish you above all is that the love which has brought you together and has made your relationship as beautiful, humane and decent as any I have encountered, will accompany you throughout your lives, help you to surmount all adversity with ease and be the making of your happiness. I rejoice wholeheartedly over your marriage because I know that you cannot he anything but happy in your life together and that — after you have been joined together — neither of you will be disappointed in the other....As you know, of all my brothers and sisters, I loved you the best and you were the one in whom I always had most confidence-so you will believe what I say, without any need for solemn asseverations and unnecessary verbiage.
Surviving letters from Engels to Emil Blank often seem to have a monetary underpinning. For example, this one, from 3 April 1846:
Dear Emil,
Be so kind as to send me £6 — or approx. 150 fr. — by return of post. I shall let you have it back in a week or two. My old man isn’t sending the money I was expecting on 1 April; apparently he intends to bring it with him when he comes for your child’s’ christening. But I've now got 150 fr. worth of things in pawn which I must redeem before my people arrive and therefore must have that amount at once. ....
And this one, from March 1848:
Dear Emil,
After the glorious February revolution and Belgium’s stillborn March revolution, I came back here last week. I wrote to Mother asking for money so that within a few days I could return to Germany[208] where we are starting up the [Neue] Rheinische Zeitung again.
...........The simplest thing would be for you to send me 20 pounds in banknotes, these being highly regarded here, and at once arrange with my old man to reimburse you. In this way I shall get my money quickly and be able to leave, whereas I would otherwise be stuck here for another week.....
You can send half of the bisected banknotes to me today, addressed to 19ter rue de la Victoire, Paris, and the remainder next day to Mlle Félicité André, same street and No. This will foil letter thieves.....
......
My kindest regards to Marie [Blank] and the little ones and reply by return.
In haste,Your
Frederick
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