@IdiotsIdiotsEverywhere you sound like my worst nightmare.
I cross the road and walk 2 miles out of my way to avoid walking past people like you. Pushy, opinionated, controlling, snide, and judgemental. Not a great mix, and it's hardly surprising people don't want to spend time with you. Especially with the vitriolic remarks you have made about people wanting to spend time with their family! I mean God forbid people want to be with their OWN family! 
I agree with many of the posters on here. When people say they are busy, and have plans, and they keep saying it, it's because they don't want to see you. If I had plans for the weekend, and someone I LIKED asked me to meet up, I would say 'awwww I'm so sorry I'm busy, but what about next weekend instead?' I would offer an alternative weekend, (if it was someone I wanted to see.)
If it's someone I don't like, and don't want to see, then I will keep saying 'sorry I am busy... / I have plans....' And as many posters have said, I don't have to explain why.
If someone is constantly putting you off then it's obvious that they don't like you. I can't believe you can't see this. Everyone else can!
@multicolourmophead
What I hate about telling people my plans is that sometimes they'll say "I'll see you there" and when you get to the event, or whatever, that other person/family has been deliberately seeking you out at said event and latch onto you. When I'd wanted to go by myself/with my family for our little outing. I sometimes want to do things without being someone else's entertainment.
Yeah this too. DH and I have told people (we are not keen on) what our plans are, and they turn up! On top of turning up, they also cling on to us, and follow us around, and stop us mixing with others, and also stop us just sitting together as a couple all evening (if that is what we want to do!) We end up feeling obliged to talk to them.
As has been said, if someone isn't telling you what they are doing, they don't want you to know, they don't want to see you, and if they are going somewhere, then they DEFINITELY don't want you there.