I’ve been growing these two pots of allocasia regal shield all winter long. They are in 6 inch pots. I’m planning to put these in large planters outdoors for the summer. They will be the thriller to other perennials and annuals in the planter. I’m hoping to put them in grow bags within the large planter of other plants so that it’s easier for me to bring them indoors again for the winter later. My question is whether I should put these two together in a 3 gallon grow bag or put them individually into 1 gallon grow bag.  also, will these plans do well in grow bags?
The plant you have, Regal Shields, is one of the larger ones and can easily reach 6 feet tall with 3 foot leaves, especially when brought outside in summer. The mature plant will require a 10-gallon container at minimum. Your plants seem to be in very small pots now, so I would pot them up first into pots an inch or two larger and the upscale later in the season. They do love to be a bit potbound.
Thus, the grow bag idea is not the ideal solution. In addition, they have very specific soil and environmental requirements.
They like to be moist but not soggy, so regular watering is critical and good drainage even more so! Make sure the container has several drainage holes and is not terra cotta because it dries out quickly. Use a potting mix specially formulated for alocasia, or a high-quality all-purpose potting mix , PLUS materials to improve drainage such as orchid bark, perlite, vermiculite or coco coir.
They prefer light shade.
You can surround them with annuals that like the same conditions, such as Coleus, Plectranthus or Helichrysum.
Here are some resources for additional information on the care and maintenance of this big, beautiful plant: