I imagine you are busy so whatever you add needs to be short time wise.
I am thinking something along the lines of fact of the day. Select one thing to teach them each day and weave it into your day to day activities. Aim for encyclopaedic knowledge. For instance maybe you might choose to teach them about insects. On Monday you show them different types of insects in a book, Tuesday you show them how many legs they have, Wednesday show them the three body parts, Thursday find some in the garden and talk about habitiat, Friday count some insects, Saturday review the book talking about what you learnt this week. Sunday well lets face it with twins you are bound to need a catch up day!
during the week show them all the words in Spanish as you go.
The idea is to build their knowledge of the world around them one topic at a time, weave your math and reading into it and work of the children's interests. Maybe they love trains, or monkeys, or the weather.....
Continue doing what you are doing already as it is a solid base. Doing in something like this will give you purpose to your days and you will feel like you are teaching them something at least. IMPUT IMPUT IMPUT sometimes its hard to see the IMPUT youa re doing when you do it so often it becomes routine. You are doing plenty already