If you want them to stay small then keep them in a pot. If you want them to grow large plant them in the ground. Plant them now if want to do it this year. It will give them some time to adjust before it gets warm. For all my trees, including guava, I try to keep the soil moist but not wet. My guava grew like weeds in the first year. About 5x their size in one year.

I spent almost 10 years in Asia mostly in Taiwan. I enjoyed every exotic fruit I tried except two. One was the jujube and the other was the rock-hard, non-sweet green guava that all the locals seemed to enjoy and that you seem to have growing in your backyard. My Taiwanese wife grows them here in south Orange County, CA and I still don`t "get" them. Give me the soft, pink fleshed Hawaiian type guavas that I grow here, too any time. I also like strawberry guavas.

If they are from different seeds, they will pollinate each other. They should be grown in separate pots because the stronger one may choke out the other one. Even though they are from the same plant, genetically they are slightly different and so that's why seedlings can pollinate each other. Exact clones (cuttings) are 100% genetically the same so there would be pollination issues. I say different seeds because some plants (I'm not sure if pineapple guava is one) are polyembryonic - many embryos / seedlings from the same seed (Blue Lilly Pilly is an example of poly embryonic-seeds) Think of this as identical twins (poly-embryonic) and fraternal twins (seeds from the same plant) The other seedling may survive - pot it up separate and see. No harm in trying.

Keep in mind that the name "guava" is used for a number of different species. I have been growing the so-called "tropical" guava (Psidium guajava)? It flowered earlier in the summer and is now covered with the fruits. Don't know quite what to do with them--I know people are crazy for this tree and its fruit in Latin America. I don't have room in my house for many of the plants so I keep a lot of them in my two-car garage that I use as a greenhouse. It faces due South, the top two rows are all glass so it gets tons of sun--especially in the winter. The guava is the most tender plant that I have in the garage over the winter, so if it's okay, I know all the others are fine. The minimum temp is usually around 40 F in the dead of winter on really cold days and maximums may only be in the upper 40's . I don't recommend these low temp for the tropical guava but it came through the winter with all its leaves and is fruiting now so it is a tough. (I've even had one loose all its leaves come back in the Spring!) The "strawberry guava" is more cold tolerant than P. guajava and would probably appreciate a cool location when you overwinter it inside. Hope this helps. Good luck!