2. Technically if you are both travelling on the same itinerary then you need all the miles required for the upgrade in one account. However if you call Emirates they should be able to split the booking for both of you and you should be able to upgrade separately using your individual miles.

If your miles are not enough to upgrade the entire trip then it might be wortwhile trying to see if you can upgrade one of the sectorswhich needs lesser miles. . Does DXB SEZ need lesser miles than GLA DXB. Upgrading each sector separately costs more miles though than upgrading tge whole GLA DXB SEZ in one go. But its not a bad idea if the miles are about to expire anyway. I have also noticed that sometimes there could be avaialability on one of the sectors individually but no upgrade availability for the full trip.

3. The 25000 limit applies to purchased miles AFAIK. (It does not matter whether you purchased them or whether someone else gifts it directly to your account). There is no limit on transferred miles though.Technically someone else can buy the miles into their account and transfer them to your account but then you will be hit buy the cost of purchase and then the cost of transfer.