Correct, all GFS restore points are full backups. If you need separate incremental chains for each retention level, then you need a separate backup jobs for them. (Though chances are monthly and yearly incrementals will be comparable to full backups in size, die to the amount of changes occurred).
I do not see an issue with the monthly job, since you can select months explicitly. So the only issue here is with the weekly job that shouldn't run on the first Sunday of the month, but this can be addressed with the help of scripting.