Hi 
Bit of background to our situation: I'm a SM to an almost 3 year old girl who me & my partner have between 3-4 nights a week; sometimes more if we take her on holiday/her mum goes away/her mum is ill etc - but that's the average. She attends a nursery local to her mums for her 15 free hours per week, but her mum has recently started working full time, so either my mother or I have her during the week (I'm going in to my final year at university but I've had a longhand period of summer holidays and I only work weekends due to no extra shifts at work) and we either keep her overnight or drop her back off at her mums, depending on what suits everyone best.
Believe it or not, we actually all get along quite well. My partner and my SD's mother were never together (one night stand) but they try and co-parent, and she also has a partner who lives with her.
Ok, now that's done - here's my dilemma. I've recently found out that I'm pregnant (almost 16 weeks) & my partner had decided that he's going to start studying at University (he's 25, but never went when he was 18 due to personal circumstances) and is due to begin his course in 2 weeks - meaning he'll only be working part-time.
Now, we're going to be very tight for money, which we're well aware of. We live with my parents (don't want to fall into the rent trap) so won't be entitled to any help from the government I don't think, so will be surviving on our student loans, my SMP and partners part-time wage. We provide everything for my SD when she is here - pull ups, clothes, food etc and we also pick her up/drop her off a good 25 minute drive away to her mums each time that we have her as her mum doesn't drive.
Despite us having her near enough half the week each week (sometimes more), SD's mum has asked for £15 per week to help towards SD's living costs. My partner is debating this, but I do sympathise with her as I know that she's struggling - she recently booked a holiday to Mexico for 3 weeks with her partner for next April which was really expensive (SD will be staying with us and the baby) but didn't realise that most of her benefits would be taken away when her partner moved in, and she has been dropping a few hints here and there about being short for cash because of it for a few weeks now, so we were expecting this.
We've already decided that we're going to set up a savings account for our baby and hope to but £5 a week each (so £20 a month each) into this in the hopes of never touching it and giving it to him/her when they are 21. My dilemma is that I wanted my partner to do the same for his daughter as I don't think that it would be fair for us to do this for our child - and any more children that we have in the future - but not do the same for her. However, there's absolutely no way that he can afford to give £15 a week to SD's mum and put money away in savings for her when he'll be working around 14 hours per week on minimum wage whilst he's studying.
So, sorry for the long waffle - but what should we do?! I don't think he would have to give her £15 p/w if she went to CSA due to how much we have her/how little he'll earn etc, however that's not really the point, is it... The choice is either to give the £15 a week to her mother or put it away in a savings account for her, and we just don't know what to do 
TIA for any suggestions.