Hi, we have been in a similar situation to yourself and know exactly what you are going through. Beau started showing aggressive behaviour from around 18 months, guarding and unpredictably biting (always my oh). We are lucky in that we live in rural France and only had children around for holidays etc and we could kennel him at those times. At around 2 yrs or so we came to the same sad point as yourself, that is last chance sort it or he has to go. After much research on the internet we decided to try him on a 5-htp supplement, along with much stricter ground rules (not allowed on laps, beds, settee , house line at all times, etc). It took about a month for aggressive behaviours and body language to noticeably diminish and then a while longer before we felt comfortable around him, and so it continued peaceably for the next 18 months or so. He was still a bit of a guarder and reactive to noises but not a major issue.
We stopped the 5-htp recently but his behaviour markedly worsened over the weeks until he bit the oh again, so he is back on it permanently and fingers crossed he continues to behave himself, it seems to work for us.