「姉さん、も朝なの」と言った。
いちは長太郎の布団の側に行って小声で言った。
「まだ早いからお前は寝ていなさい。姉さんは、 お父さんのことで出かけなければならないよ。」
「それならおいらも行く」
と言って、長太郎は起き上がった。
「じゃあ、起きて。着物を着せてあげよう。長さんは小さくても男だから、
一緒に行ってくれればその方がいいから。」
The question may sound trivial, but I want to ask if we can replace the bolded sentence with
一緒に行ってくれればいい or 一緒に行ってくれればいいから
and the possible change of the meaning.
There are some online examples go like
一緒に行ってくれればいいじゃん。
一緒に行ってくれればいいのに。
They wouldn't be interchangeable.
一緒に行ってくれればその方がいいから
if you (thankfully for me) go with me, it's better一緒に行ってくれればいい
一緒に行ってくれればいいから
it'll be enough/nice if you (thankfully for me) go with me
Here are three points:
方が introduces comparison, where Japanese adjectives cannot inflect themselves into the comparative grade.
What その (=it) refers to in the first sentence is the previous clause, or "your going with me", while such interpretation is hard to make in latter sentences, as maybe you can feel from my somewhat literal translations above. That's also partly because...
V + ばいい is actually a common idiom or construction, which represents a kind of grammatical mood, whose English rendering would vary from "comfortable with —" to "the only thing one has to do is —". There are plenty of posts on this site regarding this phrase:
一緒に行ってくれればいいじゃん。
一緒に行ってくれればいいのに。
Are you asking if these particles at the end are possible alternatives? If so, no neither.
～から: Literally "because", but as you may know, expresses an intention of persuasion at the end of a sentence. If need to be translated, would be like "you see?"
～じゃん: Colloquial, or even vulgar slang that exactly means what English tag questions e.g. "isn't it" mean.
～のに: At the end of a sentence, indicates a sort of nuance that usually conveyed by subjunctive in English, such as "if only —" or "(you) should've —".
In this context, none of those other final particles fit in, though 一緒に行ってくれればその方がいいじゃん？ (uptalkedly) would be barely valid, if the story were set in the present day.
