All piglets should have colostrum from their mother. After that you could think on fostering a litter. Regardless of the birth weight is more important to have the same 4-5 hour difference in farrowing time. Not because the piglets are in the same farrowing room, you could try fostering separated litters of differente age (in hours). For you is 1 day, for the piglets are 24 hours of age difference.