Everyone in a plural system can be non-verbal, or some folk may be verbal, semi-verbal or non-verbal.
This article is a Stub.
Some folk in a plural system may not be able to be verbal. Some systems or system members may be non-verbal due to dissociative or anxiety blocks on being able to speak, though there are plenty of other reasons.
Non-verbal folk (full system or individuals) can find adaptive technology although for some reason (perhaps because frustrated parents are willing to throw money at a problem) nearly all communication board apps are extremely expensive compared to other apps that provide adaptive technology features.
However there is an amazing website for learning ASL for free, if that's of assistance for y'all or your loved ones: http://lifeprint.com/ is a huge free resource site and there's full video ASL classes for free. The intent may be mainly for teaching able folk ASL, but the online classes at least appear intended for adults, and look like they use a similar curriculum to Signing Naturally by Dawn Sign Press (https://www.dawnsign.com/series/details/signing-naturally).
There is a very long Twitter thread "post-a-day" (not really every day) that highlights non-verbal folk both just doing what they do, or addressing abled people and allistic people about being non-verbal. https://twitter.com/ekverstania/status/1095803838462918656
Other resources for non-verbal folk and those who champion them include activism resources and human rights campaigns regarding allowing people to communicate in their own personal best way possible. These include https://unitedforcommunicationchoice.org/ and https://communicationfirst.org/ which may be helpful, in terms of activism, and perhaps some resource lists and links to other sites, or have materials that would be helpful.