I would certainly, while you are stuck at home and can't do anything to practically support DH just yet (until you know to travel or not), start to think about useful things you could do.
So DH, you and DS will all need clean and suitably formal outfits for the funeral in due course. Do you all have something suitable in your wardrobes? Does anything need cleaning or mending or replacing? And by "formal", I don't necessarily mean full on black dress and veil for you or suit for DS - but clean, neat, and respectful outfits (DS might well be fine with a pair of neat jeans with no rips and either a shirt or a plain jumper or plain top over that, and probably with shoes rather than runners - but school shoes would be fine if he has those (some schools don't have uniforms so many DCs only have runners). So just mentally (or even physically) review your various wardrobes. And clean or send to dry cleaners anything you think may be needed soon.
Food. Savoury meals - tasty, not adventurous more comforting and filling types of meals, and transportable if you are a distance away. Or to put in the freezer to be able to have tasty food easily at home - as you may end up doing a lot of travel for the next short while, and needing food when you are rushing.
Also snacks - there may well be an outpouring of baking locally to DMIL, but biscuits, buns or loaf cakes are always useful. And small things that can travel are particularly useful, especially if you and DH have to do a lot of travelling.
Could you organise a grocery shop for them?
They may be fine - but that could be something that, if they need it, you could do online and arrange delivery (in line with when they (DH/DMIL/DBIL) say someone will be at home). Things like milk, tea, coffee, sugar (for themselves and visitors), sliced bread, things to make sandwiches (ham, cheese, whatever they might eat), breakfast items, and something easy to make a dinner (good ready meal or very easy to cook ingredients) - preferably that could also be frozen if not needed just now.
You know that you find these discussions difficult.
So write down a few things for yourself - sorry for your loss, hope you are doing ok in the circumstances, is there anything you can do etc?
And also the questions that you think you need DH to answer -
Sorry for your loss
How is everything?
What do you want or need me to do?
Would you prefer me (and DS) to come now, at the weekend, or for you to come home first and we go up later?
Do you need spare clothes, money, phone charger?
Is there anything I can do here to help - any phonecalls I can make etc?
Do you have any idea when I can expect to see you (up there or down here at home), or is there a lot to sort out before that?
Take the time to think about the information that YOU need, and frame the questions for DH. You might be able to talk to him, but you might only be able to have a text conversation if he is very busy. So you are trying to let him know that you want to help and not make things more difficult, but you also need to be guided by him about what is best.
And definitely be prepared for all sorts of emotions.