Do you have any other level 60s on your other 3 accounts in addition to the 2 level 60 Hunters you have on 2 of your 5 accounts?
It sounds like one level 38 alt is a Hunter, what class is the other level 38 alt?
Out of party mains can't damage/kill the tagged mobs till the mobs are level 48+ or the XP will be greatly reduced.
If your level 38 alt can effectively tag level 48+ mobs then the mains should be able to contribute to killing them though you likely would need effective ranged tagging by the alt with quick interception by the main(s)/pet(s) or your alt(s) will die a lot. I am not sure how dying may affect the XP rewarded if your mains kill a tagged mob after your death... You may need to do some testing and do some tags where you stay alive and see if the XP is higher. One option would be to have the level 60 pet(s) attack one 48 mob in a group and screech on the others and then let your alt tag them. You will lose XP on the one mob but the mobs should ignore your alt as your pet has AoE aggro and you should be able to safely tag the rest with your alt... Please report back your findings on XP awards differences between death and staying alive.
One option is to continue tagging lower level mobs with your 2 alts and then killing the mobs with both alts and the 2 Hunter's pets (only the pets) until level 48+ mobs are safer/easier to tag by your alts.
1 day played to get 2 alts to level 38 is pretty darn good so another option would be to power level 2 more alts to ~38 (so essentially 2 days played to get 4 alts to 38) and then group those 4 level 38 alts with a single level 60 main to get an
effective team level of 42 and then kill appropriate level mobs with the full 5 man team as a single party (Approach 1).
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