MySQL using up all RAM and SWAP in group replication settings

To switch of MySQL engine you could :

1 Make a ALTER TABLE myTable ENGINE=InnoDB

2 Make a mysqldump of your table, then edit the CREATE TABLE statement to replace MyISAM by InnoDB and restore the dump in the new table (i called it myTable_InnoDB):

DROP TABLE IF EXISTS `mytable`;
CREATE TABLE `mytable` (
  `id` int(11) DEFAULT NULL
) ENGINE=MyISAM DEFAULT CHARSET=latin1;

.

DROP TABLE IF EXISTS `mytable_InnoDB`;
CREATE TABLE `mytable_InnoDB` (
  `id` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

Best regards

You can't configure a MySQL server to connect to multiple masters as a replication slave.

You can configure Master B with log_slave_updates enabled, Master A with binlog_format = ROW and declare table 2 using Engine=BLACKHOLE on Master B, and the replication events from Master A's binary log will cascade through Master B onto Slave C, which would be connected only to Master B (not directly to A).

Otherwise, your alternative is Multi-Source Replication in MariaDB, which (unlike Oracle MySQL) does allow a single server to connect to multiple upstream masters simultaneously, as long as there are no conflicting combinations of schema+table names being replicated. This configuration should work whether the master servers are actually running MariaDB or if they're running MySQL.