Both Serjilla and Al Bara are reachable from Aleppo or Hama by a combination of taking regular public microbusses and hitchiking the last stretch. Take a microbus to the town Ma'aret an Nu'man, and switch to another microbus headed for Kefr Nabl from there.
Once there, its probably best to ask for walking directions, and start walking the road to Serjillah. Try waving down any vehicle that goes in the same direction, chances are very good they will offer you a ride free of charge.
The same approach works for the way back, and anyone taking you for a ride is likely to drop you off somewhere on the microbus route. Make sure to head back in time though, these microbusses cease operation as early as 4 pm.
The Simeon Monastry can be reached in similar fashion from Aleppo. Take a microbus for Daret'Azze and walk/hitch a ride from there.
Note that Aleppo has several bus stations closely laid out in a cluster, and it can be a daunting task to find the correct point of departure for your destination. The best source of information are people that work at the stations food/drink vendors, drivers. Some will try to sell you an expensive chartered vehicle ride, but many are helpful and will point you in the right direction.
