I heard that Lara Tybur is a royal family / royal blood. Can Eren activate the power of founding titan when they touch each other since the Warhammer titan has a royal blood? Thanks for answering.
According to the wiki page, they are said to be of "noble" blood, but not necessarily royal:
The Tybur family (タイバー家 Taibā-ke?) is a house of Eldian nobles living in Marley as honorary Marleyans.
They were allegedly opposed to King Fritz and were also fighting for the power of the Nine Titans. Logically speaking, this wouldn't make sense if they were also of royal blood, as they would inevitably get the power of the Nine anyways.
So to speak, the Tybur's are not of royal blood, and Eren couldn't have used the Founder's ability while making contact with Lara. If she was of royal blood, I have no doubt that he would enact the Rumbling.