import re

pattern = r"\b[a-zA-Z]{1,2}(?:\.[a-zA-Z]{1,2}){2,}\b"
texts = [
    'a.b.c',
    'ab.c.dd.ee',
    'a.b',
    'aaa.b.cc'
]

for s in texts:
    print(re.sub(pattern, lambda x: x.group().replace(".", ""), s))