This is a very tough one. You may not be privy to what is going on in their lives, so what you deem a normal income, may NOT be enough to cover emotional needs of which you are unaware. I will give you an example.
Someone makes on paper what appears to be a decent income, not well-off, but not poverty stricken, either. The family cannot afford to go on vacations EVER, or fix up their home, and such. But they CAN afford to go out to eat once a week. Someone remarked to me that if they wouldn’t go out, they might have enough money for those other things. But their going out is what keeps them from feeling like paupers on a regular basis. Are they managing their money the best way? Maybe not, but it is not our business to judge.
If you don’t feel comfortable giving them money, for the reasons you mentioned, then you probably shouldn’t. If you will resent them, it diminishes the chessed. It might be a great thing to find a money management class of some kind and mention that are going to it to help yourself with your own money issues because you feel you could learn some helpful tips for yourself, and would they be interested in joining you. Get a few couples together, so they don’t feel it is directed at them personally. Maybe this could be done in someone’s house, with a nice collation. In my opinion, that would possibly get the point across without singling them out. You could even tip off the speaker to address certain issues in a roundabout way v’hamyvin yavin (hopefully). JMO.
BTW, I totally understand where you are coming from on this. I know someone who used to be wealthier and now is not, but who continues to spend money on things I (and most people, I would bet)consider to be unnecessary (weekly manicures, waxing, etc), as she did when money was readily flowing. This comes out to hundreds of dollars each month, that could be saved. But maybe that’s what she needs to keep from feeling poor.