Yes, love it!
But I only have a 15.1.
I would not want to tow two 16.2+hh with it.
We have towed a 15.2 TB and a 14hh chunky monkey together - it didn't feel noticably different to towing the one.
I find it mostly handles like a car, not a tank.
My sister has the Terracan, which is an ugly big brute but will pull two 17.2hh monsters without noticing... though she said it did struggle in bad ground with tose on board!
We have one and tow a 505 with a 16.1 sports horse. i wouldnt tow much heavier though. We want to get a 510 so bea has a little more space but it may be a little close to the maximum towing capacity, so she will have to wait until its time to change cars again.
If i remember correctly it tows 2200kg. I think our one has a bigger engine than the one your looking at.
What i would be careful off though is the servicing is really expensive on them, but all in all my mum loves that car!!!
So in answer to your question, its probs would tow a 510 and 17.1 but whether it would be advisable i dont know, i personally wouldnt
You'd be right up there on the limits - and there's always going to be the temptation to offer a lift etc. to someone with a space in a nice big trailer... I'd be cautious.