Where is LV's lair? (Hide Out) with an apparation question

[quigonginger]

No: HPFGUIDX 87316

In wondering where LV's lair might be, Steve (bboy_mn) pointed out:
 
> Malfoy Manor has one major problem, I don't think Draco can be 
trusted
> with the secret, in addition, I'm not sure Malfoy is in a position 
to
> have escaped Death Eaters wandering in and out at all hours of the
> day. 

I (Ginger) snipped the rest to reply:

I agree totally with your concerns about Draco.  Mr Crabbe and Mr 
Goyle wouldn't draw much attention by visiting, but if Bella or even 
LV himself showed up, the little twit would probably faint dead away, 
and then brag to the Slyths about how they had had tea.  Making sure 
Harry could hear, of course.

I have to wonder about the DE's wandering in and out, though.  Which 
brings me to my question:  What limitations are there on apparating?  
We know one has to be liscenced (or ought to be), but are there any 
limitations as far as apparating into a house?  The only one we see 
is Arthur, but he apparated into his own home.  At 12 Gimmauld, 
people come to the door.  

I imagine this is just good manners, and that people also have 
security charms in place to prevent uninvited visitors.  What I 
wonder is whether or not people can just apparate into another 
person's house, assuming they have permission.  

This would solve the problem with the DE's coming and going.  They 
could just apparate into a certain room set aside as LV's office (or 
den or library, or whatever).

It also would have been a nice way for Sirius to have gotten out once 
in a while.  He could have visited the homes of Order members for tea 
every now and then, and by apparating into their living rooms, no one 
would have been the wiser. 

Ginger, who thought much on Sirius tonight