The answer depends on the level, but generally members of a multiverse ensemble have little or no gravitational effects on each other.
Level I spatially infinite multiverses have normal gravity: each local copy of some material configuration has the same gravity, and would affect each other were they close enough - but practically they only interact with nearby spacetime.
Level II inflationary multiverses have inflation domain bubbles affecting each other along the spacetime manifold, but most of their contents are very far from a domain boundary and hence never feel anything.
Level III many-worlds interpretation of quantum mechanics: normal gravity inside each branch, but two parallel branches do not interact gravitationally.
Level IV ultimate ensembles: not every mathematically possible universe has gravity, and hence they cannot interact with each other gravitationally.