I'm going to join in it, as long as everyone is going to participate in it.
I'm going to join it, as long as everyone is going to participate.
「みんなが参加するなら参加します」
Points
1 Join in /participate in /take part in
「参加する」
全て同じ意味です。
2 As long as 〜「もし〜なら」
As long as you are with me, i can do it.
「もしあなたが一緒なら、できます」
To say you will join in on an event you can also say i'll participate/join or take part they all mean the same.
By saying 'as well; it means others are too (as well as me)
So you can say I'll join in/take part/participate/take part) as long as everyone else does as well'
イベントに参加すると言う場合、「I'll participate/join/take part」と言えます。全て同じ意味です。
「as well」と言うと、「（私と）他の人も」という意味になります。
ですので、以下のように言えます。
I'll join/take part/participate/take part, as long as everyone else does as well.
（皆が参加すれば、私も参加します。）
The two sentences you see provided above are terrific ways to express to your listener that you will participate in something as long as everyone else participates as well. In the first sentence you will see the phrase follow suit. This phrase means to follow another persons actions. This is a phrase that is common in our everyday conversation and it would make a great addition to your vocabulary.
The above format is the most normal in the UK. It is a standard phrase and uses the First Conditional structure to indicate an option dependant upon a condition.
Form: If + verb in present simple + Will (or future tense)+ verb
上のフォーマットがイギリスでは最も一般的です。標準的なフレーズで、条件を示す仮定法現在を使っています。
形式：
If ＋ 動詞の現在形 ＋ Will（または未来形）＋ 動詞
All three of these are acceptable ways to express the same idea. A way of saying that you will participate is to use the phrase, "join in," which indicates that others are already engaged in an activity and you will now engage in the same activity with them. Also, saying "so will I" shows that you will do the same as someone else or as a group.
3例とも言っていることは同じです。
参加することを表す一つの言い方として「join in」があります。これは他の人たちがすでに行っていることに加わるというニュアンスです。
また、「so will I（私もそうします）」も、他の人と同じことを自分もすることを表します。
I will consider going if everyone else is going too.
I won't go if everyone else doesn't. I"ll only go if they are too.
When you want to explain that you would only go to an event/party if others are willing to go too; then you may explain it in the following ways:
-I'll go if everyone else does too.
-I will consider going if everyone else is going too.
-I won't go if everyone else doesn't. I"ll only go if they are too.
パーティー/イベントについて、他のみんなが行くなら自分も行くと伝える言い方です：
【例文】
-I'll go if everyone else does too.
［訳］みんなが行くなら私も行きます
-I will consider going if everyone else is going too.
［訳］みんなが行くなら私も考えます
-I won't go if everyone else doesn't. I'll only go if they are too.
［訳］みんなが行かないなら私も行きません。みんなが行くなら私も行きます
These are two pretty simple options to express what you want to say. I personally use the first option, although, there is no big difference between them, so, choose any.
日本 
イギリス 
アメリカ合衆国 
南アフリカ 
カナダ 
