RewriteEngine On

RewriteCond %{HTTP_HOST} subdomain1\.domain\.com
RewriteRule ^aaa([0-9]+)\.html$ /subdomain1/index.php?page=$1 [L]
RewriteCond %{HTTP_HOST} subdomain2\.domain\.com
RewriteRule ^bbb([0-9]+)\.html$ /subdomain2/index.php?page=$1 [L]
RewriteCond %{HTTP_HOST} subdomain1\.domain\.com
RewriteRule ^(.*) /subdomain1/$1 [L]
RewriteCond %{HTTP_HOST} subdomain2\.domain\.com
RewriteRule ^(.*) /subdomain2/$1 [L]