¿Tienes comprados los globos y las velas, o quieres que los compre yo?

Both are possible, but they are not exactly the same.

• ¿Has comprado los globos y las velas? simply asks whether you bought them.
• ¿Tienes comprados los globos y las velas? focuses on the resulting state: whether you already have them bought and taken care of.

So tener + past participle often suggests something is already done and settled. In English, it can sound like Do you already have the balloons and candles bought?

This structure is very natural in Spanish when talking about preparations, arrangements, or tasks already completed.

Because comprados agrees with the whole group los globos y las velas, not just with velas.

When Spanish has a mixed-gender plural group:

• masculine + feminine together → masculine plural

So:

• los globos y las velas → comprados

If the noun phrase were only feminine, then you would use compradas:

• ¿Tienes compradas las velas?

In this sentence, comprados is a past participle behaving very much like an adjective.

That is why it changes form:

• comprado
• comprada
• comprados
• compradas

It agrees with the thing that is already bought. This is different from the perfect tense with haber, where the participle does not change:

• Has comprado los globos
• not has comprados

So here:

• tienes comprados los globos y las velas

means something like you have the balloons and candles in a bought state.

Because after querer que with a different subject, Spanish uses the subjunctive.

Here the subjects are different:

• quieres = you want
• yo compre = I buy

So Spanish says:

• ¿Quieres que los compre yo?

not:

• ¿Quieres que los compro yo?

The form compre is the present subjunctive of comprar.

A useful rule:

• same subject → infinitive
  
  • ¿Quieres comprarlos? = Do you want to buy them?
• different subject → que + subjunctive
  
  • ¿Quieres que los compre yo? = Do you want me to buy them?

Los refers to los globos y las velas.

Since Spanish uses the masculine plural for a mixed group, the pronoun is los, not las.

So:

• los globos y las velas → los

This is the same reason the participle is comprados.

Yes, Spanish often leaves subject pronouns out, but here yo is included for emphasis or contrast.

The sentence is contrasting:

• you buy them
• or I buy them

So yo helps stress that contrast:

• ¿...o quieres que los compre yo?

Without yo, the sentence is still grammatical:

• ¿...o quieres que los compre?

But with yo, it sounds more like:

• ...or do you want me to buy them?

Yes, absolutely. That would be a very normal sentence too.

The difference is mainly one of nuance:

• ¿Has comprado...? = Did you buy them?
• ¿Tienes comprados...? = Do you already have them bought / is that task already taken care of?

The version with tener + participle often sounds a bit more focused on preparation and whether something is already sorted out.

Spanish often uses definite articles where English would not.

Here, los globos y las velas sounds natural because it refers to specific items already understood in the situation, such as party supplies.

So Spanish prefers:

• los globos y las velas

where English might simply say:

• balloons and candles

Dropping the articles is sometimes possible in certain contexts, but in this sentence the version with articles is the most natural.

It would not change the basic meaning, but it would make the idea of already more explicit.

For example:

• ¿Ya tienes comprados los globos y las velas...?

This sounds like:

• Do you already have the balloons and candles bought...?

Even without ya, the structure tener + participle already suggests completion, so ya is optional and mainly adds emphasis.

It is used in Spanish generally, not only in Spain. A native speaker from many Spanish-speaking regions would understand it perfectly.

That said, frequency and style can vary a bit by region and by speaker. Some people may more often choose a simpler form like:

• ¿Has comprado los globos y las velas...?

But tener + participle is a normal and useful structure to learn because it appears often when talking about things that are already done, prepared, or arranged.