I believe antibiotics would be a good preventative even if you’ve treated their wounds externally.
Also, what will prevent a second attack this evening? They need to be all inside a secure location, or you need to be absolutely sure you know how their coops were breached and have fixed it. A weasel will kill and wound indiscriminately, and can fit inside a tiny hole. Also suspect would be a raccoon, possibly a possum.
Dose: Important - You need to know their weights! From this post, dissolved and given orally by needleless syringe. 200 mg/kg orally, twice per day. Also electrolytes given because amoxy reduces available potassium
https://www.backyardchickens.com/posts/26704465/