Should one obey his mother even if she was wrong?

Obeying one`s mother is mandatory in matters that are beneficial to her and as long as she drive her children to commit sin.

What is the ruling when a woman forsakes her husband in bed because he doesn`t pray regularly?

I am a disabled woman who has vaginal discharges and can`t control her urine. Therefore, I combine prayers. Is that permissible?

All perfect praise be to Allah, The Lord of The Worlds, and may His peace and blessings be upon our Prophet Muhammad and upon all his family and companions. According to the Hanbali doctrine, it is permissible for the sick to combine prayers. In your case(Asker), it is better that you delay the noon prayer until a few minutes before the afternoon prayer in order to minimize the time span between the two and perform each alone. In addition, you can do the same with sunset and evening prayers. Finally, we ask Allah to bless you with recovery. And Allah knows best.

What should the man, whose wife wasn`t on good terms with his mother, do?

Both the mother and the wife have rights on the man in question; therefore, each should be given her rights justly, and he should resort to wisdom to please both of them and make reconciliation.