Is it permissible for a wife to boycott (not to attend to his different needs) her husband?
It isn`t permissible for the woman to boycott her husband unless he is the reason behind that, and it is recommended that both spouses seek the advice of righteous people to make reconciliation.
What is the ruling on a Friday sermon in which the khaṭīb did not explicitly exhort the congregation to be conscious of Allah (taqwā) in both sermons, but sufficed with commanding them to obey Allah and refrain from disobeying Him?
All praise is due to Allah, and peace and blessings be upon our master the Messenger of Allah ﷺ.
For the Friday sermon (khuṭbat al-Jumʿah) to be valid, certain essential pillars (arkān) must be fulfilled. Among these is the exhortation to be conscious of Allah (waṣiyyah bi-taqwā Allāh), which must be present in both sermons. Alongside this pillar, the praising of Allah (ḥamdallah) and the sending of blessings upon the Messenger of Allah ﷺ are equally required.
Shaykh al-Islām Imām Ibn Ḥajar al-Haytamī, may Allah have mercy upon him, states: "These three are pillars in each of the two sermons, because each sermon is independent and separate from the other." [Tuḥfat al-Muḥtāj,Vol.4/P.447]
It is not a condition that the exhortation be expressed in any specific wording, nor is it required that the word "taqwā" itself be used — such as saying "I exhort you to be conscious of Allah." Rather, this pillar is fulfilled by any expression that contains a command to obey Allah the Almighty and to abstain from what He has prohibited.
Imām al-Khaṭīb al-Sharbīnī, may Allah have mercy upon him, states: "The third pillar is the exhortation to taqwā... The specific wording of this exhortation is not required, according to the most correct view, because the purpose is admonition and the urging of obedience to Allah the Almighty. Therefore, any expression that conveys admonition suffices — whether long or short — such as: 'Obey Allah and be ever mindful of Him.'" [Mughnī al-Muḥtāj,Vol.1/P.550]
Accordingly, what the khaṭīb has done — by commanding obedience to Allah and forbidding disobedience to Him in both sermons — is valid and sufficient. And Allah the Almighty knows best.
What is the ruling on using moisturizing creams on the skin during the day in Ramadan?
Using moisturizing creams on the skin does not break the fast because they do not enter the body cavity (jauf). Any absorption that occurs through the skin pores does not count as entering through an open passage.
Is it permissible for a woman to wear underwear while performing Umrah?
Yes, it is permissible for a woman to wear underwear while performing Umrah. This is because she should keep her regular clothes that cover all her body while being in a state of Ihram (ritual consecration) for Hajj, or Umrah. However, she should uncover her face and hands, but it is permissible for her to let her head-covering garment drape from her head down over her face when non-Mahram (i.e., marriageable) men pass by her. And Allah Knows Best.