Should the worshipper raise his hands when standing up from the first Tashahhud, if the Imam's last Tashahhud is the worshipper's first Tashahhud in a four-rak'ah prayer? And should he raise his hands if he caught one rak'ah and sat for the last Tashahhud with the Imam?

Raising the hands in prayer is established at the opening takbir, and when bowing and rising from it, and after rising from the second rak'ah. What a latecomer (masbuq) catches with the Imam is, according to the preponderant opinion, the beginning of his prayer; meaning, what you caught is considered the start of your prayer, and what you missed you complete. So, if you catch the first tashahhud in a four-rak'ah prayer, the Imam's third rak'ah is the first for you, and the rak'ah you stand up for after the Imam's taslim is the third rak'ah. As for raising the hands when standing up to complete the prayer, it is recommended if the standing is for the third rak'ah. Scholars differed regarding raising the hands in other instances where the latecomer stands up to complete his prayer: some link raising the hands to standing for the third rak'ah, while others link it to standing up from tashahhud in general.