Эти туфли красивые, но у них слишком высокие каблуки.

Yes. Эти means these.

It agrees with туфли (shoes), which is plural, so Russian uses the plural form of этот:

• этот = this (masculine)
• эта = this (feminine)
• это = this (neuter)
• эти = these (plural)

So:

• Эти туфли = These shoes

Туфли is the plural form of туфля (a shoe), but in practice Russian often talks about shoes as a pair, so the plural is very common.

So:

• туфля = one shoe
• туфли = shoes / a pair of shoes

In this sentence, we are clearly talking about a pair, so туфли is natural.

Because it describes туфли, which is plural.

Russian adjectives must agree with the noun they describe in number, gender, and case. Since туфли is plural nominative here, the adjective is also plural nominative:

• красивый = beautiful (masculine singular)
• красивая = beautiful (feminine singular)
• красивое = beautiful (neuter singular)
• красивые = beautiful (plural)

So:

• Эти туфли красивые = These shoes are beautiful

Both forms can be predicate adjectives, but they are used differently.

• красивые is the full form
• красивы is the short form

In modern everyday Russian, the full form is much more common in sentences like this:

• Эти туфли красивые. = natural, common
• Эти туфли красивы. = grammatical, but more literary or formal

So a learner should usually default to красивые in normal speech.

Because Russian usually expresses possession with у + genitive rather than with a direct equivalent of English have.

Literally, у них слишком высокие каблуки is something like:

• at them are too-high heels

A more natural English translation is:

• they have heels that are too high
• or their heels are too high

This у + genitive pattern is extremely common in Russian:

• У меня есть книга. = I have a book.
• У неё красивые волосы. = She has beautiful hair.
• У них слишком высокие каблуки. = They have heels that are too high.

Because after a preposition, Russian personal pronouns change form.

The preposition у requires the genitive case, so они becomes них:

• они = they
• у них = of them / at them

Also, after many prepositions, Russian adds н- to third-person pronouns:

• у него
• у неё
• у них

So у они is not possible.

Yes, you can think of есть (there is / there are) as being omitted.

Russian often leaves out есть in the present tense when possession is clear from context.

So these are both possible:

• У них есть слишком высокие каблуки.
• У них слишком высокие каблуки.

But the version without есть is more natural here.

Because a pair of shoes has two heels, so Russian uses the plural:

• каблук = heel
• каблуки = heels

So:

• высокие каблуки = high heels / high heels on the shoes

In this sentence, it means the shoes’ heels are too high.

Yes, literally it means high heels or tall heels.

• высокий = high / tall
• каблук = heel

In shoe-related context, высокие каблуки naturally means high heels.

So the second part means that the shoes are nice, but the heels are too high.

Слишком means too in the sense of excessively.

It usually goes before the adjective or adverb it modifies:

• слишком высокие = too high
• слишком дорогой = too expensive
• слишком быстро = too quickly

So:

• у них слишком высокие каблуки = their heels are too high

Because но means but, and in Russian it normally joins two clauses, so a comma is used before it.

Here the two parts are:

• Эти туфли красивые
• но у них слишком высокие каблуки

So the comma works just like in English:

• These shoes are beautiful, but their heels are too high.

A useful breakdown is:

• Эти — nominative plural
• туфли — nominative plural
• красивые — nominative plural
• у них — них is genitive after у
• слишком — adverb
• высокие — nominative plural
• каблуки — nominative plural

Why nominative for каблуки? Because in the possession structure у них ... каблуки, the thing possessed is typically in the nominative:

• У меня книга.
• У неё машина.
• У них каблуки.

So них is genitive, but каблуки stays nominative.

Yes. Красивые can mean beautiful, pretty, or nice-looking, depending on context.

So possible natural translations include:

• These shoes are beautiful, but their heels are too high.
• These shoes are pretty, but the heels are too high.
• These are nice shoes, but the heels are too high.

The exact English choice depends on style, not on a grammar difference in the Russian sentence.