Question

2. las sillas de ti. su sillas

3. el hermano de mí. su hermano

4. la computadora de tu y yo. mi equipio ya usted mismo

10.No he ___dormio___(dormir) en días.

13.Lo he ___pones___(poner) en tu mesa.

15.Tienes razón, lo he ___dije___ (decir) en broma (You are right, I said it as a joke)

Answer 1

Where are the instructions of what you are to do? If you are working with possessive adjectives, here they are: first in Spanish (and then in English)

mi, mis (my = note one is singular and one is plural, depending upon the noun it modifies)
tu, tus (your...)
su, sus (his...,her...its...their)
nuestro, nuestra, nuestros, nuestras (our)
vuestro, vuestra, vuestros, vuestras (your, being familiar plural, which is not taught in all textbooks)
su, sus (their + singular noun, their + plural noun)

Now, guessing at what you are to do:
2. tus sillas
3. mi hermano
4. IF this is to say "your and my computer" = tu y mi computadora OR nnuestra computadora (our computer) Besides what I see is incorrect with the prepositional pronouns. Here they are:
de mí (my)
de ti (your)
de él/ella, Usted (his, her/your)
de nosotros, nosotras (our)
de vosotros, vosotras (your)
de ellos, ellas, ustedes (their/your)

It looks like you are trying to do a SHORTCUT by not showing me the INSTRUCTIONS, MODEL SENTENCE THAT YOU SEE. Without those things, I can not be sure what you are to do.

Beginning with #10, the minute I see "he" (I have)( it tells me you require the Present Perfect tense, which is a form of "haber" as the helping verb + a past participle.
haber = he, has, ha, hemos, han
past participles that are regular look like this for -ar, -er, -ir verbs
hablar = hablado
comer = comido
vivir = vivido

When you put the 2-part verb together, it is something like: he vivido = I have lived / has comido = you have eaten / hemos hablado = we have spoken

10. dormido (AGAIN I'm purely "guessing" at what you are to do but have no idea what "dormio" is doing there because there is no such form!
13. puesto
15. dicho (irregular past participle)

You'd best get back with questions!

Sra