Why are numbers appearing instead of names in messenger?

When I create a new message, sometimes I can choose a name and it will appear (ex: my sister and dad) but other times it is just their number (ex: my mom and boyfriend) How can I get their names to show up on the messaging screen instead of their phone numbers?

crwdns2934089:0crwdne2934089:0 crwdns2934093:0crwdne2934093:0

crwdns2934109:0crwdne2934109:0

crwdns2889612:0crwdne2889612:0 0
crwdns2934285:0crwdne2934285:0