I have DS1 (5.4), DS2 (3.0 but delayed so developmentally more like 2) & 9 w.o. DS3. Also have experience from before as DS1 was 2.3 when DS2 was born.
I find the key thing is to get out each day. Toddler groups are great as toddler can play & baby may sleep or often people want to hold them if you don't mind that. Also these places are full of other parents who are bound to be sympathetic to a screaming baby or tantrumming toddler, and there is often a cup of tea on offer
If there are no toddler groups, the park is good on a dry day or soft play on a wet day. As somebody said before, if you can do these in the morning, you can get home, have lunch, nap, play, bath, bed.
If you can't get out, now is a good time of year to get in the garden lots, if you have one. A sand/water table is great, as is a little gardening set (both my big DSes love digging in the garden),a ball & a slide, plus maybe a ride-on or Little Tikes car.
Good indoor activities are baking, colouring, puzzles, building bricks, toy trains. Plus don't be afraid to have some Cbeebies each day if you need it! Also, I have found that DS2 likes to 'help' with the housework, so will pass me things from the dishwasher, follow me around with his own dustpan & brush etc.
Final thing - playdates. If you know anybody with DC the age of yours, suggest meeting up with them & you can have a coffee & a chat & DC can totally ignore each other play together. If you go to each other's houses, at least the DC will have new toys to play with once in a while, iyswim.