Answer:
Mi familia es grande. Tengo veinte tíos y veintisiete primos. Tengo más tíos que mi mejor amigo. Mi mejor amigo tiene quince tíos. Su novia solo tiene seis tíos. Ella tiene menos tíos. Pero ella tiene once primos y mi amigo tiene once primos también. Ella tiene tantos primos como él.
To select ther right words, you need to analyse the context. The person who is talking, has more uncles that his friend, that's why we need to use "más" and "que", because that's the way to do the comparison.
Then, he says that his friend's girlfriend as less uncles that him, but she has the same number of cousins than his boyfriend. So, we indicate thta with "tantos" and "como", it's the right way to express the equivalence there.
