OP, I have read all the thread, but it was so back and forth and I'm in a rush, so I may have got the wrong end of the stick - so apologies for that if I do.
Christmas is always alot of pressure whether you are hosting it, going to family etc etc. I've been married 19 years and only last year did we get an immediate family only Christmas as home. This year will be the same (hopefully!).
If SIL wants to duck out of presents I would suggest just go with it, even if its annoying. I personally love giving presents as its my way of showing someone they are special and I've thought about them, but for some people its just not that important or a priority, and at the end of the day if they are skint they are skint. I think you should try and understand that. Yes you might see them spending money on other things but at the end of the day its up to them to decide how to spend their money. Would you want them analyzing and judging what you are spending your family's money on? You and I don't really know what money pressures or priorities they have, so I'd just step back and give them a break on this.
While I love giving people presents and surprises, I don't really understand why there is such pressure over Christmas presents - one year we even did no presents for ourselves but donated present money giving to charities where it could make a real difference around the world.
Marriage is a compromise. And Christmas is a pretty difficult one because there is always alot of pressure to be with family, or do it a particular way etc.
I think you already said you and DH have reached a compromise that you go to your DM who will chauffeur you back and forth? If he has compromised about that, then you should compromise about not going to stay overnight. Yes, I understand it would be easier, and would mean your mum not cooking and driving, but at the end of the day he has already agreed. There needs to be give and take on both sides. Perhaps when he sees it in practice he would be more reasonable another time?
Can I say that the suggestion you have Christmas at your place next year is sensible. By that stage your little one will be crawling or walking and into everything. Often its alot easier in your own home where everything has been child proofed to the appropriate age of your child.
You and DH need to have a sensible discussion about Christmas Eves, Days and Boxing Days. You are about to have your own family. I would just say, don't get into the trap of it always being a certain way (unless of course you both feel the same). I have cooked Christmas Dinner including when I had young babies for 17 years. DH cooked twice once when I had done my knee in, and once when he said he wanted a cheaper Christmas (but ended up spending more because instead of making everything he bought it all). That's partly because I'm a good cook and like your MIL I like things done in a certain way - although I would appreciate more help.
We have always hosted it at ours and I did all the cooking for family or friends.
Sit down with your DH and decide how you will both make your own traditions. It may include compromise on both your parts. I'd be thinking of alternating his family, stay at home and your family in whatever order you want to do it. You may find you also want to think about hosting sometimes (but I wouldn't get trapped into it every time you spend Christmas at home). Remember also you will have a young baby, then a toddler etc. Children have different needs at different times in their lives, and you may find that Family plans for a particular year don't always mesh with your needs as a family.
I'm glad to hear that your DH can cook dinners (it was abit misleading when you said he couldn't cook - I too felt that sense of feminine outrage about lazy men!). Even if you ended up having Christmas at home, I don't see why it would be a problem with him cooking, or even sharing (better) the task between you. If either he or you haven't done a Christmas dinner before (I'm not sure of that but getting that feeling - sorry if I'm jumping to conclusions), you sometimes just have to bite the bullet. I understand if you stayed at home this year, you would have a young baby - but it is perfectly possible especially if you plan, cook and freeze in advance - I've done that with Christmas food (though not the meat), and with vegetarian food when we've had vegetarians coming.
Hope you work it out!