  Core accretion and disk instability require giant protoplanets to form in the
presence of disk gas. Protoplanet migration models generally assume disk masses
low enough that the disk's self-gravity can be neglected. However, disk
instability requires a disk massive enough to be marginally gravitationally
unstable (MGU). Even for core accretion, a FU Orionis outburst may require a
brief MGU disk phase. We present a new set of three dimensional, gravitational
radiation hydrodynamics models of MGU disks with multiple protoplanets, which
interact gravitationally with the disk and with each other, including disk gas
mass accretion. Initial protoplanet masses are 0.01 to 10 $M_\oplus$ for core
accretion models, and 0.1 to 3 $M_{Jup}$ for Nice scenario models, starting on
circular orbits with radii of 6, 8, 10, or 12 AU, inside a 0.091 $M_\odot$ disk
extending from 4 to 20 AU around a $1 M_\odot$ protostar. Evolutions are
followed for up to $\sim$ 4000 yr and involve phases of relative stability ($e
\sim$ 0.1) interspersed with chaotic phases ($e \sim$ 0.4) of orbital
interchanges. The 0.01 to 10 $M_\oplus$ cores can orbit stably for $\sim$ 1000
yr: monotonic inward or outward orbital migration of the type seen in low mass
disks does not occur. A system with giant planet masses similar to our Solar
System (1.0, 0.33, 0.1, 0.1 $M_{Jup}$) was stable for over 1000 yr, and a
Jupiter-Saturn-like system was stable for over 3800 yr, implying that our giant
planets might well survive a MGU disk phase.
