Humus I will answer your question and then answer the general question from KeyserSophie "For those who wouldnt consider it, do you mind me asking why not?" and together they may explain my position in respose to the OP.
Hummus the OP clearly does not want to think about this now and her dh is being selfish putting this on her now. IF it was all so important to him he should have discussed this before marriage or before a baby came along. Maybe the OP would have chosen not to have a baby with him if she had felt relinquishing him for six weeks a year, from age 12, was part of the plan.
Her dh married her, perhaps they met in the UK, where he had already set up a life. Is that the case Strawberry
He has no right to expect this arrangement just because he comes from South Africa IMHO. not unless he specifically said this is how it would be, which I am guessing he did not.
South Africa is not a very safe place to live. I would not want my child there without me. I have a friend from South Africa, she and her dh live in the UK now, and her sibling moved to another country. They visit (my friend, her dh and kids) every few years and the relatives visit them.
If I were in the OP's shoes I would consider this, visiting as a family. There are lots of countries I would not feel happy to visit, let alone leave my child in. Parents get to choose not to do these things and not to be pushed into them by their partner. If the OP was from North Korea or one of the hot spot war torn areas of the world, would her husband be fine with the kids going there? There are lots of places people may not like to visit, for all kinds of reasons.
KeyserSophieparents get to choose, but it's rather nice to hear people say how they spent summers in Italy or whatever, (much closer than South Africa and I would imagine much safer) and of course any family that wishes to do this, great, fine, up to them.
I am answering for me, we do not have extended family anywhere more than about 3 hours drive away! If we did the key things for me would be:
Did my kids have a good enough relationship with the relatives to live with them for a number of weeks?
Would I trust the adults do a good job in loco parentis?
Would they want?
Am I happy/are they happy to work hard all year and for my kids to be busy with school each term and then for summer holidays to come round and me not to see them and them not to see them?
I'd rather spend money on nice holidays to see the relatives with my kids, why does the DH wish to send his son rather than spend some time with his own mum? Yes, work etc tricky but in the end as an adult I want to cultivate and continue relationships with my and dh's family as well as them cultivating relationships with the kids.
My kids would not wish to do this, I know that, won't bore you with the details, and my in-laws are nearly 80. They had a fab day with kids yesterday but a week would knacker them out, let alone longer.
Lastly, my kids like their friends and their home and would not want to be in different home for weeks on end. But we all know our own kids, don't we. Except the OP, whose child is a month, and her dh is badgering her to agree to something in 12 years time.
I think the OP has the usual, a dh problem not a MIL problem.
I'd tell dh to stop talking about it, we will think in future. Say same to MIL, Not agree to anything.The lovely tinkering with cars/running through fields future some children may have had may not be the case for this family, why can't he build a car with his own father one day?
I love my in laws, I loved my parents when they were alive. But they had their chance to be parents, and their role is to love and support their kids and grandkids and not to make demands which are unreasonable, IMHO.