Well, I'm no pilot...heck I don't even have my PPL yet...but I'll do my best to give you as much info as I can
1.What kind of flying you do,i.e. shorthaul/ longhaul and what is your typical weekly/ monthly routine?
It really depends on the company you work for and what aircraft you fly. If you fly 747s for British Airways, then you will most likely fly long flights. If you fly 737s for British Airways, the flights obviously won't be as long as if you flew the 747s.
2.How often do you have to work at weekends?
When you first start off with the company, you will have a low senority number and you usually won't get the flights that you want. That means that for your first few years, you will be stuck with all-nighters, weekends, and flights to the middle of no where...pretty much the flights that no one want. after a while as you build your way up the ladder, things will look brighter.
3.How much time do you have to spend away from your families, say over a month period? Can this cause problems?
again, when you first start out it will be a lot of time away from home stuck in hotel rooms eating out a lot. I think I read somewhere that the new pilots fly about 20 days a month or so..don't quote me on that though.
4.How much spare time do you have in comparison say with someone who works a regular 9-5, Mon-Fri job?
Well assuming that you fly 7 hours a day, 4 days a week, you will have some extra time off compared to other people. However, those 28 hours may be mostly day, so even if you do get more free time, it will be during the day when you want to sleep...it all depends on many different factors.
5. Is it a sociable job, do pilots socialise/ go out drinking much with each other?
From what i've heard they do...a real airline pilot can give a better answer to that.
Once again, I'm not an airlines pilot, this is just from what I've heard over the years from my brother (737 FO for Alaska), and other pilots.