Lia fratino loĝas sur la dua etaĝo, sed ilia patrino loĝas sur alia etaĝo.

Lia means his, while ilia means their.

So:

• Lia fratino = his sister
• Ilia patrino = their mother

A learner may notice that this could mean the sister belongs to one male person, while the mother belongs to a group of people. In context, ilia patrino often means their mother in the ordinary family sense.

In Esperanto, a possessive like lia, ŝia, ilia, mia, and so on usually takes the place of la.

So you say:

• lia fratino = his sister
• ilia patrino = their mother

Not normally:

• la lia fratino
• la ilia patrino

This is similar to English, where we say his sister, not the his sister.

Loĝi means to live or to reside somewhere.

So:

• Lia fratino loĝas... = His sister lives...
• Ilia patrino loĝas... = Their mother lives...

This verb is specifically about where someone resides. It is not the same as simply being somewhere.

Sur usually means on, and in Esperanto it is commonly used for floors of a building:

• sur la unua etaĝo = on the first floor
• sur la dua etaĝo = on the second floor

So Esperanto treats a floor as something you are on.

English does something similar: we often say on the second floor, not in the second floor.

Dua means second.

Esperanto forms ordinal numbers with -a:

• unu = one → unua = first
• du = two → dua = second
• tri = three → tria = third

So:

• la dua etaĝo = the second floor

Here dua is an adjective describing etaĝo.

Because la dua etaĝo refers to a specific floor: the second floor.

But alia etaĝo means another floor or a different floor, which is not being identified exactly.

Compare:

• la dua etaĝo = the second floor
• alia etaĝo = another/different floor

If you said la alia etaĝo, that would mean something more like the other floor, referring to a specific one already known from context.

Alia means other, another, or different.

In this sentence, sur alia etaĝo means that the mother lives on a floor that is not the second floor mentioned earlier.

So the idea is:

• the sister lives on the second floor
• the mother lives on some other floor

Because they are adjectives.

In Esperanto, adjectives end in -a:

• dua = second
• alia = other / another
• bona = good

They describe nouns, and here they both describe etaĝo:

• dua etaĝo
• alia etaĝo

Possessives like lia and ilia also behave like adjectives, which is why they also end in -a before nouns.

Because nothing here is a direct object, and the phrase with sur is describing location, not movement toward somewhere.

In Esperanto, -n is often used for:

1. a direct object
2. motion toward a place

Here we have location:

• loĝas sur la dua etaĝo = lives on the second floor

That is static location, so no -n is needed.

If there were movement, you might see -n, for example:

• Ŝi iris sur la duan etaĝon. = She went to the second floor.

Sed means but.

It connects the two clauses and shows a contrast:

• his sister lives on the second floor,
• but their mother lives on another floor.

So sed tells you that the second part differs from the first in an important way.

It is normal and straightforward Esperanto word order.

The pattern is basically:

subject + verb + place

So:

• Lia fratino = subject
• loĝas = verb
• sur la dua etaĝo = place

And then again:

• ilia patrino = subject
• loĝas = verb
• sur alia etaĝo = place

Esperanto word order is fairly flexible, but this sentence uses a very standard, easy-to-follow order.