Hello and thanks for the query.
Since there is blood and mucus in the stool, there is a possibility of infection. This may need some antibiotic.
Kindly take the babies to a good hospital, rather than private doctors. A stool evaluation needs to be done and your babies will be examined completely for weight, growth, and other problems before getting appropriate treatment.
Also ensure proper sterilization
of bottle and nipple and use separate sets for each baby to prevent further transfer of infections from one baby to another.
Hope you are reassured. Take care.