From this article:
学校を経営している会社は、教育と関係がある会社のほかに、不動産や介護、建設などの会社も増えています。
[companies that run schools] Besides companies related to education, companies involved in real-estate, nursing and construction are also increasing.
I cannot parse this sentence. The topic 学校を経営している会社は seems to be unrelated to the rest of the sentence.
First of all, the cultural context that needs to be understood in order to fully comprehend this sentence is that in Japan, it is not rare for companies to start a sideline business that is totally unrelated to its original line of business. Japanese language schools are often started by non-education-related companies.
(学校{がっこう}を経営{けいえい}している会社{かいしゃ})(A)は、(教育{きょういく}と関係{かんけい}がある会社) (B)のほかに、(不動産{ふどうさん}や介護{かいご}、建設{けんせつ}などの会社)(C)も増{ふ}えています。
The basic structure of this sentence is:
"A consists not only of B but also of C."
More specifically,
"Among A, there is B and additionally, there is also an increasing number of C."
Thus, the topic (A) is perfectly related to the rest of the sentence.
"Found among the companies that run the (Japanese language) schools (today), are education-related companies and additionally, an increasing number of companies involved in real estate, care for the aged, construction, etc."
Well, the topic (as you have identified) is "companies that run schools"; the sentence is talking about such companies, and says that [these; the topic] are not only companies (directly) related to education, but also increasingly, companies from the real-estate, nursing (or rather, "care workers", I think) and construction.
