I did 2 issues already. Anyway
Before posting the first issue, I made the Armour Stands (with the tags I used ) hold a spawn egg and a dragon head, The spawn egg was in his offhand, and it is above the normal position (Middle of it's arm) I'll put the command and image below. It was a shulker egg (I got it from a command generator to find out what it was) and I tried to search what number it's data is, but it shows as a dull white spawn egg.
/summon ArmorStand ~ ~1 ~ {ShowArms:1,Small:1,Invisible:1,Invulnerable:1,NoBasePlate:1,NoGravity:1,HandItems:[{id:spawn_egg,Damage:69,Count:1},{id:skull,Damage:5,Count:1}]}
The dull shulker egg is because spawn eggs now use nbt rather than data values
Ps you didn't give it a lefthanded tag and it's in the right arm, so it's in the main hand, not off hand