When is に needed and when can it be omitted in がある constructions?


Someone asked me about the meanings of two English phrases. I replied:

> 両方はたくさんの意味がありますから、文がないと具体的な説明が難しいです。

Almost instantly it hit me that I might've made some mistakes in that reponse.
I know the standard response goes:

> どっちにもいろんな意味がありますから、文がないと具体的な説明が難しいです。

So do I need the「に」and「も」? I know what they mean and why they are there. Those
are the basics. I am just wondering if my version could actually work in
colloquial language, since「は」foregrounds the topic.

**Edit** : When can「に」be omitted? Because we do say

> 私は仕事があるんで、
>
> 私は今日は仕事がありません。

Why can 「に」be omitted here?

Also I wonder if my choice of「両方」sounds too formal in this sentence.




両方 is fine, 両方は sounds unnatural. I'd say 両方とも is about the most natural.
どっちにも and どっちも are both fine.

**EDIT:**

> 私は仕事があるんで、
>
> 私は今日は仕事がありません。
>
> Why can 「に」be omitted here?

You can add に here, but then it emphasizes that YOU have work but others have
not. Depending on the context it might even sound accusing. For example:

> 「どうせ誰が落としたんだか分からないんだから、この財布いただきましょうよ」  
>  「僕には良心があるんで（あなたには無いようですね）」

僕は良心があるんで is more neutral here.

> What about 両方にも and 両方には

両方にも doesn't work here because it implies there is some third thing that also
shares the situation, but there isn't any in this context (valid example:
長男にはほくろが多い。次男と次女にもほくろが多い).

両方には can work, although it sounds a bit too formal for spoken language. E.g.
you wouldn't say 長男にはほくろが多い in spoken word unless you really want to emphasize
only 長男 has ほくろ (but if you are writing it's completely fine to use it for a
neutral context).

If you ask me why 長男はほくろが多い works but 両方はたくさんの意味がある doesn't work, I can't
clearly explain it, but maybe for は to work there needs to be a single actor.
E.g. 両方向は物知りだ sounds very unnatural. 方向は物知りだ is still unnatural but much
better. 方角は物知りだ sounds OK. IMO this is because 方角 can be imagined as an actor,
while that is a lot harder for 両方向.

