[A.A. Cunningham]

Scripture tells us that Peter was married at one time. Scripture does not mention his wife.

One can’t have a mother-in-law unless one is married.

Again, Scripture only tells us that Peter was married at one time. If my wife dies and her mother does not, I will still have a mother-in-law. It's a very simply exercise in logic.

Your knowledge of the topic at hand is quite deficient but go ahead and be content in your ignorance.

[Catsrus]

It is you who is ignorant. Its also possible that Peter took his wife with him at times according to 1 Corinthians 9:5:
5 Do we not have the right to take along a believing wife,[a] as do the other apostles and the brothers of the Lord and Cephas?

One must look at Scripture in light of other Scripture, therefore, avoiding Biblical error by taking one out of context