when viewing the bridal party as a guest it was girls to the left, guys to the right - simply because that's how it had been during the ceremony - the celebrant made sure that, when we looked back to the crowd after the ceremony, i was at DH's right hand.... we just let that flow through to the ceremony

with regards to your sisters bub - i'd invite her - we didn't have a restriction on kidlets at our wedding simply because it was a biggish venue and the catering costs were very reasonable - but if we'd had to restrict the number of children there, my bro's kids still would have been invited - they are immediate family and i wouldn't have offended bro by saying no to his kidlets! the youngest of the three was 17 months old - and they all behaved amazingly well!! your friends will understand your sister having her bub there - it's not like you're saying friend A can have bub there, but friend B can't - siblings are very different to friends!

the boyfriend/girlfriend thing - we sent our invites out 8 weeks before the wedding - there were only a few friends that weren't married or in extremely long term relationships - so we looked at their personal situations - if they'd been with their partner more than 3 months, they were invited - but we didn't put "and partner" - we asked for their partners name (under the guise of wanting to start getting place cards and things organised around the same time as printing the invites...) - we didn't have anyone there that we didn't know previously (apart from the fact we put the band on one of the tables as they'd travelled for a few hours to be there, and were friends of a friend - so we gave them a feed!)

good luck with it all hun!