Мы часто ходим к ним в гости.

Because часто shows a repeated, habitual action.

• ходить = to go regularly / repeatedly / in general
• идти = to be going right now, in one direction, on one specific trip

So:

• Мы часто ходим к ним в гости = We often go to visit them.
• Мы идём к ним в гости = We are going to visit them now / we’re on our way.

In the basic verb system, yes, ходить is the verb for going on foot.

However, ходить в гости is also a very common expression for going to visit people, and speakers often use it without strongly focusing on whether they walked or not.

If you want to emphasize travel by transport, Russian can also use:

• Мы часто ездим к ним в гости = We often go visit them by vehicle / we often travel to visit them.

So for learners, it is best to remember ходить в гости as a standard idiomatic phrase.

К means to / toward, and with people it often means to someone’s place.

The preposition к requires the dative case.

The pronoun они changes like this:

• nominative: они = they
• dative: им = to them

But after a preposition, third-person pronouns usually add н-, so:

• к ним = to them / to their place

That is why Russian says к ним, not к они, к их, or к им.

В гости is a fixed expression meaning to visit someone as a guest or over to someone’s place.

So ходить к ним в гости is not just go to them in a physical sense. It specifically suggests a social visit.

Common patterns are:

• идти в гости = to go visiting
• ходить в гости = to go visiting regularly
• пригласить в гости = to invite someone over

This is a very common question.

• в гости is used with motion toward a visit
• в гостях is used for being there as a guest

Compare:

• Мы идём к ним в гости. = We are going to visit them.
• Мы у них в гостях. = We are at their place as guests.

So in your sentence, there is movement toward the visit, which is why Russian uses в гости.

Because в гости is an idiomatic expression, and the plural form is just part of that expression.

You do not need to interpret it literally as multiple guests in English. Russian simply says:

• в гости
• пойти в гости
• пригласить в гости

So this is best learned as a whole phrase.

Yes. Russian often leaves out subject pronouns when the verb already makes the subject clear.

Since ходим already means we go, you can say:

• Часто ходим к ним в гости.

That is perfectly natural in the right context.

Including мы can make the subject more explicit, add contrast, or simply sound a little clearer depending on the situation.

Yes, you can, and it can mean We often go to their place.

But в гости adds an important nuance:

• к ним = to them / to their place
• к ним в гости = to visit them socially, as guests

Without в гости, the sentence is a bit less specific. You are still going to them, but the reason is not stated as clearly.

No. Russian word order is flexible, although some orders sound more neutral than others.

The most neutral version here is:

• Мы часто ходим к ним в гости.

Other orders are possible:

• Часто мы ходим к ним в гости. — emphasizes often
• К ним мы часто ходим в гости. — emphasizes to them
• В гости к ним мы часто ходим. — also possible, but more marked

So the meaning stays similar, but the emphasis changes.

Both can be translated as We often visit them, but the nuance is different.

• Мы часто ходим к ним в гости = We often go over to their place as guests; this sounds social and friendly.
• Мы часто навещаем их = We often visit them; this focuses more on the act of visiting the people themselves.

Навещать can be used in many situations, including ones that are not really social-hosting situations, such as visiting someone in the hospital or checking in on a relative.

So ходить к ним в гости is usually warmer and more specifically about going over to someone’s home.