Whether or not the plants are 'choking' each other would be a function of how congested the roots are in the entire soil mass. Root congestion restricts growth because the soil becomes packed with 'conductive' roots, roots the primary function of which is to move water and nutrients, rather than to gather them. This leaves a reduced volume of soil to support the fine hair roots that do all the real work. The 'center' you refer to would be called the 'crown'. If the roots have filled the pot and are restricting growth, you should consider repotting/root pruning or separating and repotting the plants in the future, but winter is a poor time to consider work as major as that. Instead, wait until early summer when the plant(s) have gained some energy and they are better able to tolerate the stress. If the smaller plant is an offset from the larger, you can simply cut them apart with a longitudinal cut so each has a healthy portion of the root system. Dust the cut with powdered sulfur if you want, to help thwart any rot organisms that might want to wreck your day. If the plants are individuals, tease or cut the root mass apart to separate the plants & repot. Don't be afraid to cut the plants back and prune roots. This type of treatment forces growth from cells closer to the root systems, which are ontogenetically younger (juvenile) and more vigorous, which is where the term rejuvenation pruning comes from. Al

I haven't seen that problem before but was wondering whether it might be from something in tap water. Rainwater is best. They're an epiphyte (and lithophyte) from rainforests, mostly growing on trees with no soil and roots exposed to the air.

I agree, those brown lines are spores. Your problems start from the fact that this fern is an epiphyte or a lithophyte. In other words they grow on trees or on rocks. The most covering the roots usually get is from the moss growing around them. In the rainforest type of environment they naturally grow in there's usually high humidity with frequent rain and water never sits long around their roots. Hence, as Rhizo has stated, the signs of chronic over watering. You need to treat it as an epiphyte.

These plants are naturally epiphytes/lithophytes growing on trees or rocks, not in soil. They live in higher rainfall areas and regularly get drenched but water drains away very rapidly. An epiphytic orchid mix , bark, or the like that will drain instantly is best so that you get air again around the roots afterwards. I regularly water mine from above to let water run over the leaves and down into the crown. With the very good drainage there's no problem with that as it keeps the root area moist and not wet. Another thing to look at is your water. Rain water is best, tap (town) water it depends on what the local authorities put into it and whether it naturally has a high mineral content.