Hi
I've two boys aged 3.8 and 2.2. 18mth gap. Things are much easier (though still v challenging at times) now the baby is a little older.
The main focus of our day is getting through it with as few arguments/fights/rows as we can manage. Structure the activities a little, if they're getting bored with something tidy it away and bring something else out. Housework can be caught up on after the children are in bed. Which is very difficult as you will be knackered but I often put my iPod on and race round for an hour trying not to sing too loudly!
We have groups of toys - drawing, painting, play do, crafty things, car mat cars & garage, train sets & trains, aqua draw, duplo, jigsaws, books, tool bench, toy kitchen, musical instruments, orchard toys games (red dog blue dog & shopping list are fab), other wow toys. I find if we try to focus on an 'activity' and then switch when they start to get bored, they're more content.
We also have a dog so will be out in all weather. Get out as much as you can.
Daytime baths are a great help, particularly if the kids are grumpy.
I've heard a few pieces of advice along the lines of, to avoid shouting its really important to engage with your children, have fun with them and build the relationship while improving communication as this should make them more likely to listen to you when you need them to. Easier said than done.
Above all, try to enjoy them and don't stress too much about housework. 