If a Planet have 2 Moons (so suppose system of 3 bodies) and we say "One Moon is tidally locked to Planet" how can we say that it is tidally locked when Baricenter of 3 bodies has its trajectory?
Tidal locking just means that one side of the Moon will face the planet all the time. The period of rotation around its own axis is the same as the period of rotation around the planet. It is not absolutely "locked" exactly in that configuration, but on average the two periods will be the same. Another moon or two could possibly also be in the same condition, and there wouldn't be strong interference between them. There could be some slow processes that could work against both remaining tidally locked, or some slow processes that kept them that way, but it's a complicated problem