My dd started staying at mine at 2 every other w/e . They can be manipulative at 2 !
I found the following would happen.
Me : ok sweetie time for bed ( insert something dd didn't want to do )
dd : Want mummy. Want mummy's house.
She'd then look at me to see my reaction.
I know all kids are different, but mine would only roll out the line about going back to mummies when things weren't going her way. And initially I did find it upsetting until I spoke to some Mumsnetters who reassured me it was par for the course. And dd clearly wasn't distressed as such.
If she'd have genuinely been in distress I would have considered taking her back to mums, and in the early stages her mum and I discussed the possibility that I may, over one weekend take her back if she was really unhappy, but it's never happened/ ( dd did once threaten to walk home to mummies, all 30 miles :) two minutes later she was happy as pie )
The only time dd has seemed genuinely upset has been a couple of times at night when she's woken up, possibly had a bad dream, probably clocked the less familiar surroundings and cried for mummy.
But lots of hugs and reassurance has put her at rest. I just see it as part of parenting. Calm her, reassure her she'll be going back to mummies, mine seems to like me singing to her if she's having a bad night )
I think one can see what is genuine upset and what is manipulation. I think as long as dad has plenty of stuff for dd to do ( paints, pencils, books, toys etc ) and takes dd out to do interesting stuff he should really be able to handle it ok.
If his place isn't child friendly at all then I could see why your dc might feel like going home to mums.