I had placenta praevia with my twin pregnancy. Like you, one of my twin placentas was low-lying. Initially partially across the cervix and then it moved slightly away but still within 'risk range i.e. within 2cm. My first bleed was at 23 weeks and my second at 25. The one at 25 weeks was quite heavy and triggered labour, which they blocked with drugs. After that I was told to take things very easy and was put on 'pelvic rest' (no exercise, no sex, no orgasms, no lifting, nothing strenuous - nothing that could cause over-exertion and/or irritate my uterus/cervix).
I'm afraid I wasn't particularly lucky as I went on to bleed further at 28 weeks and from 30 weeks was kept in hospital on bedrest whilst I bled on and off. However, I was quite unusual and unlucky as I know of people whose bleeding has either been a one-off or who have had total/major placenta praevia with no episodes of bleeding. I was just unlucky as I said. However, my twins were born at 35 weeks after another bleed and were totally healthy. They are now destructive two and a half year olds. They also avoided special care as I'd had steroids at my early labour scare to help develop their lungs. It might reassure you to know that these bleeds tend to affect you more than they do the babies - I was hooked up to monitors and being scanned during the course of one of mine and whilst I was flapping about in panic they were happily poking one another and burbling about and seemed unaware of my panic.
Once you've had a bleed you should probably be prepared for another. I don't think it hurts to have that mindset as although it's not nice to have the shadow of that hanging over you it does help to be prepared. I had a small 'bleed bag' packed, which I kept at home in case I needed to head off to hospital at short notice. It had enough for a couple of days hospital stay and included nightdress, flip flops, cardigan, small collection of mini toiletries, good book, etc. I also made sure I took my hospital notes with me when I was out and about and always had a charged mobile phone.
I'm sure you'll get lots of replies from people who've had one-off episodes of bleeding and I'd take heart from them as there is no guarantee that you will get more bleeding. The only issue is that once you've bled once then it IS more likely to happen again. Equally, the more episodes of bleeding you have the more likely they are to increase in incidence and volume - certainly this was the case with me, although this is rare.
I hope this helps and good luck with the rest of your pregnancy. Hopefully this bleed was a one off and things will now settle down - it does happen that way and there's no reason why it shouldn't happen that way for you.