Involuntary downgrade from PE to economy MCO to Gatwick

Just wanted some advice from seasoned travellers on the best way to handle this.
Booked holiday to Disney with Virgin Holidays (frequent member card holder) 16mths ago. Family of 4, myself OH and 2 children aged 9 and 13 years. Booked economy on way out but PE on return leg (£295 each for upgrade). Reserved seats 180 days prior to flight.
On way out in check in queue was offered upgrade to PE for £200 each. As myself and OH hate flying we decided to upgrade. Paid for it at seperate counter then requeued to check in at PE line. 2 hours later!!! - had sold us 4 PE seats all in different places, 1 downstairs and 3 upstairs, none together and 2 were bulk heads upstairs which meant 1 child would have to sit on their own downstairs. Still wasn't sorted but went through security had less than 1 hour in V room (which OH was really looking forward to). At gate had to wait till all PE passengers were seated so they could try and get people to switch seats. Did get all 4 of us upstairs but OH and son sat in different rows. This was all really stressful and was left wondering why we had wasted £800.
Roll forward return. As I had booked PE 16 mths early and reserved seats at earliest time thought it would be ok. Get to check in to say they were overbooked by 1 seat and as I had a different surname to OH and children they thought I was on my own so downgraded me to economy (gave my seat to a silver card holder). Was offered 300 euros which I refused as this was less than the £295 I had paid to upgrade. Again this was very stressful (I got through I whole bottle of rescue remedy!!Lol) and my 9 year old was very upset.
I understand EU law says I will get 75% of the ticket price (I assume this is the full flight price not just the PE bit - I don't know what this is though as it doesn't break this down on my invoice).
I assume this is the minimum I should get? Can anyone advise me on the best way to handle my claim with Virgin and what sort of compensation I should expect
Thanks
Booked holiday to Disney with Virgin Holidays (frequent member card holder) 16mths ago. Family of 4, myself OH and 2 children aged 9 and 13 years. Booked economy on way out but PE on return leg (£295 each for upgrade). Reserved seats 180 days prior to flight.
On way out in check in queue was offered upgrade to PE for £200 each. As myself and OH hate flying we decided to upgrade. Paid for it at seperate counter then requeued to check in at PE line. 2 hours later!!! - had sold us 4 PE seats all in different places, 1 downstairs and 3 upstairs, none together and 2 were bulk heads upstairs which meant 1 child would have to sit on their own downstairs. Still wasn't sorted but went through security had less than 1 hour in V room (which OH was really looking forward to). At gate had to wait till all PE passengers were seated so they could try and get people to switch seats. Did get all 4 of us upstairs but OH and son sat in different rows. This was all really stressful and was left wondering why we had wasted £800.
Roll forward return. As I had booked PE 16 mths early and reserved seats at earliest time thought it would be ok. Get to check in to say they were overbooked by 1 seat and as I had a different surname to OH and children they thought I was on my own so downgraded me to economy (gave my seat to a silver card holder). Was offered 300 euros which I refused as this was less than the £295 I had paid to upgrade. Again this was very stressful (I got through I whole bottle of rescue remedy!!Lol) and my 9 year old was very upset.
I understand EU law says I will get 75% of the ticket price (I assume this is the full flight price not just the PE bit - I don't know what this is though as it doesn't break this down on my invoice).
I assume this is the minimum I should get? Can anyone advise me on the best way to handle my claim with Virgin and what sort of compensation I should expect
Thanks