Samsung Kies version for both old and new android versions? A friend gave me his older Samsung tablet to upgrade since it kept failing with the OTA update, so like indicated I will try KIES first for updating the device.

However I also have 3 newer android (lollipop) phones... so ... what is the advised way? Deinstall version 3 then install version 2.6 (to work with older android versions) and after that deinstall version 2.6 and reinstall version 3 (for my newer android versions) ?

Anyone dealt with this / has a setup for this?

update I installed smart switch which seems to work for all. It calls ODIN and stuff seems to work.
If i underestand your question exactly,

OTA update is not suggested.

for many reasons, if the current installed rom from another region, maybe you cannot update it with OTA.
(perhaps, android update for your region rom not availabe)

it's better to download the Rom from Official and truted link and flash it on your phone for update.

hope this helps.