Well, they all vary, but completely normal to have to repeatedly tell a 3yo something (they're known as "threenagers" for a reason).
The majority of, if not all, behaviour at this stage is still boundary pushing/exploratory. Main thing is you're consistent in your approach to managing the behaviour (so if you say 'no', and then when it happens again 'no, if you do it again xx will happen' and then they do it yet again and xx happens as specified then it will, eventually, work). The only challenge is figuring out what strategy works for your particular child and not swapping too soon from one strategy to another.
Basically it's a long winded way of saying it sounds as though your family are judging on a snapshot when they shouldn't be and you need to ignore them and keep on with what you find to work, even if it's madly different to what they've told you to do 'advised'. Often people forget each child is different and so don't suit a one size fits all model. Might have worked for their children, doesn't mean it will work for yours.
In terms of specifics, I found the 'counting to three' strategy worked well with mine - started off with "If I count to three and you haven't stopped then xx will happen" and was able to progress (after about a year) to "I'm going to count to three" (no specific 'or else' action mentioned
) - generally I can get as far as two now and they behave.
That said, it's only what worked for mine, might not for yours. I have friends who've found success with the naughty step, others who do the 'finding things to praise' one and anything in between. The only similarity is that it took a while to find out what does work.
Good luck and please don't get too down from snippy comments. You are doing your best (and probably succeeding more than you realise too!).