Are the sins of performing prayer quickly out of respect for an elder, or delaying it out of obedience to parents, or interrupting it out of preference for friends, forgiven? And are these actions considered disbelief (kufr) or polytheism (shirk)?

What is obligatory upon you is to establish the prayer, fulfilling its conditions, pillars, and obligations. Congregational prayer is obligatory unless there is an excuse, and the mosque is not a condition for the validity of the congregation. If you complete the prayer correctly, there is no sin upon you. Abandoning congregational prayer without a valid excuse makes your prayer valid, but entails sin. Hurrying, as long as it does not prevent the completion of the prayer, does not incur sin. Abandoning some of the Tarawih prayers does not incur sin, but it means missing out on the reward. There is no polytheism in what you have mentioned. Prayer should be a priority for you, and you should pray with humility and tranquility, and associate with the righteous.