How can I get to Seven Rila Lakes from Sapareva Banya in April?

The snow level in spring is highly variable and depends a lot on the weather during the winter and also during the spring months. I might work, it might still be impossible depending on the year.

That being said, reaching Sapareva Banya will pose no problem whatsoever. This is all the time low in the valley (and not very interesting for hiking in my opinion). From Sapareva Banya the road starts to climb. This is a newly asphalted road which is kept open and should be accessible without issues. It is used by skiers.

At the end of the road there is the lift, which exists and is functioning. The hut at the upper lift station has a website with all the information (hours, prices...). Just throw that page in an online translation site.

You should certainly be able to get to that hut. From there to the lakes is something else. At that elevation there is usually still a lot of snow in April. Especially because the lakes are on the north slope of the mountains it tends to melt there slowly. If you are not confident in your abilities to deal with snow I would advise against it.

The best page to get an idea about the actual snow level is probably the Facebook page of the hut. You could also call the hut to ask how the situation is up there.

Finally, I kind of don't see the point of going there. The lakes will almost certainly still be frozen shut and covered by snow. Which means, early April, there are probably not even lakes to be seen. Just some flatter parts in the snow.