Is it OK for siblings to co-sleep? Sure!* In many cultures in the world, whole families sleep together in the same bed, out of custom, desire, necessity or a combination. If you and your husband can agree that your kids sleeping in the same bed should be your custom right now, that is great.
The AAP does not recommend bed sharing for at least the first year – this applies to babies sleeping with parents and/or siblings (even multiples). For the first year, your baby should have his or her own separate sleep space. See my Safe Sleep Checklist for more.