I had this problem a couple of weeks ago, am now down to one night feed at around 3/4am.
How I did it.
Increased daytime naps and put DS into a set routine based around school runs.
He is woken up at 7:30ish in the morning, but not fed straight away. Plays with dcs until 6:45 when we dp the school run, by the time we get home (9am) he's tired.
Feed at 9am then put him to bed. (Don't worry about feeding to sleep first just get the body clock sorted).
He wakes at 11am, has a small feed then we go to get ds1 at 11:30. Play with ds1&2 until 1pm, feed, 45minute nap.
Wake up at 2:00, go and get dd at 3:15, come home, feed, nap at 4pm.
Wake at 5-5:30, awake time til 7:15.
7:15, showerbath, feed at 7:30, bed between 7:45-8pm.
I started doing a dreamfeed at 11pm as he was waking at 1&5, the dreamfeed saw him through until about 4ish, when he would feed, then sleep until 7:30am.
But the last couple of nights no dreamfeed and he wakes between 3-4 feeds then sleeps until 7:30.
I was always a 'no-routine' person with dd&ds1 but ds2 needs routine, the other two were sleeping through by a couple of months (dd-6 weeks, ds1-10 weeks).
General rule of thumb, sleep after 2-3 hours awake, all naps a minimum of 45 minutes.