You sound at the end of you tether, thegreenlight. Obviously you need to speak to your husband and tell him that this can't continue but for now, you need a bit of support to cope with your kids who are hi-energy and disparate ages.
You've already done the baking thing. The DVD/tv can also be employed and I'm sure you are. The other thing that I've done with my kids (not such big age gaps as yours but enough) was 'sports day'. I used our garden to set up 'sports', hide-and-seek (giving each child different things to find) so that whilst there was competition there was no cheating - had them running about (timed) with different expectations based on age.
I also had sticker books, and the card game 'Memory' which is really good for your six year old if not the 2 year old. Plonk 2 year old in front of whatever they like to watch until they nod off.
Can you engage your six year old into helping you with some stuff around the house? It might be frustration on their part that their only play mate is their much younger sibling so perhaps they'd be interested in doing some tasks with you?
Other than painting/drawing - what about 'tents' in the lounge with a sheet/chairs?
It's exhausting, I know. What do they want to do? I would ask them, see what can be modified to make it suitable for both - or just let older child do what they want (within reason) and engage with the 2 year old.
I'm so sorry you feel overwhelmed. Evenings are when your husband can take over and I wouldn't bother with giving him a 'side eye', just say "I'm going up for a bath/bed/to read now" and leave him with them. No messing around or gratitude - you need time off too
And, you're not a shit mother, just a bit overwhelmed as any of us might be with all that. 