DS2 (3.9 yrs) and DS3 (2.5 yrs) are only 16mths apart so i know where your coming from (also have DS1 who is 10 and DD who is 6)......oh and i'm pg so shall be there again with you soon!
but from experience it really is important not to get yourself stressed about it as that will do no good at all, don't try and do any 'big' things like clear outs etc its just not worth it - i make a list of jobs that need doing every week (like ironing, cleaning floors, changing bedding, polishing, cleaning bathroom, vacuuming, etc) then doing 1 or 2 things a day and crossing them off the list
general stuff like tidying toys, washing, putting things away, etc i would do with them helping me as it teaches them to help you, it may take a little longer though
Once they are older they will play together more so you can do more, but for just enjoy them and do stuff when you can - housework is always there!!